Fifty-five hydrochemical monitoring points (see Figure 3- 12) have been set up in Huixian Wetland and its surrounding recharge areas to carry out on-site investigation, monitoring and research on hydrochemistry of wetlands, and conduct regular sampling and analysis. Among them, 10 points are monitored in three different periods: low water, normal water and abundant water, and the detection content includes two main indicators: organic matter and inorganic matter.
The test results (Table 3-4) show that the hydrochemical type of surface water and groundwater in wetland is mainly HCO3-Ca.
Table 3-4 Chemical Characteristics of Main Water in Huixian Karst Wetland
1) recharge area: the southern and northern parts of Huixian karst wetland are exposed pure carbonate karst areas, where surface sinkholes, karst pools, underground karst pipelines and karst fractures are developed, and most of the atmospheric precipitation directly seeps down to recharge karst groundwater and recharge the wetland in the form of rapids. Except for a few places (such as the groundwater near Mamian pyrite mine in Lingui county, which has high content and poor water quality), the groundwater is weakly alkaline, with low hydrochemical components and good water quality. For example, the chemical types of groundwater in the north of Dulong collapse pit and the northeast of Lijia collapse pit in the south of wetland are mainly HCO3 -Ca, with pH value of 7. 16 ~ 7. 18, salinity less than 230 mg/L and total hardness less than150 mg/L.
2) recharge-runoff area: this area is mostly semi-covered and interbedded carbonate karst area, and groundwater is mainly recharged by lateral runoff and vertical overflow. The development of underground karst cracks and pipelines in this area is relatively gentle, and groundwater runoff is relatively slow. The substance content and pH value in groundwater are higher than those in recharge area. Although the content of dolomite has increased, calcite is still dominant. For example, the pH value of Jiutou South Pit in Shandong Province is 7.04, and the total hardness and salinity are higher than those in the recharge area, which are 194.86mg/L and 328. 17mg/L respectively. The chemical type of groundwater is still mainly calcium bicarbonate.
3) Drainage area: The drainage area of Huixian karst wetland is mostly located in the covered karst area, mainly pore groundwater, which is generally replenished by agricultural irrigation water. Inorganic and organic fertilizers are easy to penetrate into groundwater with surface water, and the groundwater flow rate is slow and the purification ability is poor. As can be seen from Table 3-4, except for the outlet of Shizishan underground river, the pH value, total hardness and salinity of groundwater in Qixingmin well and Xiazhatang bottom well have obviously increased, and the chemical type of groundwater has also changed to HCO3 Cl-Ca K type. For example, the neutralization content of lake water in Qixingcun Wharf in Mudong is high, reaching 0.6 mg/L and 0.3 mg/L respectively, and the water quality is poor.
Second, the water quality evaluation
1. Surface water quality evaluation
(1) water quality evaluation standard
According to the Environmental Quality Standard for Surface Water (GB 3838—2002), this Standard for Surface Water Quality Assessment evaluates the surface water quality of wetlands, and it is divided into five categories according to the environmental functions and protection objectives of surface water areas.
Class I: mainly applicable to water sources and national nature reserves.
Class II: It is mainly suitable for the first-class protected areas such as centralized drinking water surface water source, rare aquatic organism habitat, spawning grounds for fish and shrimp, and feeding grounds for larvae and juveniles.
Class III: It is mainly suitable for centralized drinking water surface water sources, fish and shrimp wintering grounds, migration routes, aquaculture areas and other fishery waters and secondary protected areas in swimming areas.
Class Ⅳ: It is mainly suitable for general industrial water areas and recreational water areas where human body is not in direct contact.
Class ⅴ: Mainly applicable to agricultural water use areas and waters with general landscape requirements.
(2) Water quality evaluation method
Using comprehensive pollution index method, the formula is:
Study on karst wetland ecosystem in Huixian county
Where: P is the comprehensive pollution index of surface water; Ci is the measured concentration of pollutants (mg/l); Si is the surface water environmental standard concentration of pollutants (mg/L); N is the number of water quality evaluation factors.
See Table 3-5 for the classification standard of comprehensive pollution index of surface water.
Table 3-5 Classification Standard of Comprehensive Pollution Index
According to the Environmental Quality Standard for Surface Water, the evaluation factors are pH value, COD, ammonia nitrogen, total phosphorus, copper, zinc, fluoride, arsenic, mercury, cadmium, chromium and lead *** 12. For the purpose of protecting the wetland environment, the standard concentration of surface water is calculated according to Class III water standard in Environmental Quality Standard for Surface Water (GB 3838—2002).
(3) water quality evaluation results
The comprehensive pollution index evaluation results are shown in Table 3-6. Some surface water points in this assessment, such as the outlet ditch, sub-pond, Longdong wetland, Dulong Beishan (fish pond), Dulong-Longshan wetland and the source of Mudong River, are all located in the wetland. Xiguanzhuang Qingshui River and Dulong Farm are located on the edge of wetland; Qixing Wharf is located in the wetland population gathering area. As can be seen from Table 3-6, the surface water bodies at all points in the wetland have not reached the Class III water body standard in the Environmental Quality Standard for Surface Water (GB 3838—2002), and have been polluted to varying degrees. The main factor exceeding the standard is total phosphorus. The water pollution index of most observation points is around 0.5, slightly higher than the standard value of 0.4, which belongs to the range of mild pollution; Among them, the comprehensive pollution index of water quality in Dulong Farm and Mudong River source in individual months is 0.84 and 0.97 respectively, which belongs to moderate pollution; The comprehensive pollution index of surface water quality is only greater than 1 in individual months in the reservoir and Qixing wharf, which is serious pollution.
There is no obvious law of wetland water pollution, which may be caused by the disorderly distribution of wetland pollution sources. Many ponds and swamps in the wetland are exploited to varying degrees, and the development of agriculture and aquaculture will reduce the water quality of the wetland (Figure 3-23). Qixing Wharf is located in Qixing Village, with a large amount of domestic sewage and garbage discharge (Figure 3-24). Affected by the drainage from nearby paddy fields and fish ponds, the flow of ponds is poor and the pollution is serious.
Table 3-6 Comprehensive Pollution Index Evaluation of Surface Water Quality in Huixian Karst Wetland
Figure 3-23 Different degrees of water pollution
Figure 3-24 Quality of Domestic Sewage in Qixing Wharf
2. Groundwater quality evaluation
(1) water quality evaluation method
According to the Groundwater Quality Standard GB/T 14848-93, groundwater quality is divided into five grades.
Grade I (excellent water): suitable for various purposes.
Grade II (good water): suitable for various purposes.
Grade III (Good Water): Based on human health standards, it is mainly suitable for centralized drinking water and industrial and agricultural water.
Grade Ⅳ (poor water): According to the requirements of industrial and agricultural water, except for agricultural and some industrial water, it can be used as drinking water after proper treatment.
Grade V (extremely poor water): it is not suitable for drinking, and other water can be selected according to the purpose of use.
Groundwater quality evaluation is based on the data of groundwater quality investigation and analysis or water quality monitoring, which is divided into single component evaluation and comprehensive evaluation.
According to the groundwater quality standard GB/T 14848-93, the groundwater quality of Huixian karst wetland was evaluated by single evaluation and comprehensive evaluation respectively. The evaluation method adopts the evaluation factors of each monitoring point corresponding to the assignment range of five types of water specified in the standard, and carries out single-component evaluation (Fi) according to the principle of "which is better or worse" (Table 3-7), so as to carry out single-component evaluation of water quality. On the basis of single-component evaluation, the comprehensive evaluation index (f) is calculated by using formulas (3-2) and (3-3), and the water quality is comprehensively evaluated according to the groundwater quality classification standard (Table 3-8).
Table 3-7 Corresponding Score Table of Individual Components and Categories
Table 3-8 Classification Standard of Groundwater Quality
Comprehensive evaluation index f calculation formula:
Study on karst wetland ecosystem in Huixian county
Study on karst wetland ecosystem in Huixian county
Among them: f is the average of the individual scores Fi of the participating factors; Fmax is the maximum of the individual scores of participating factors.
According to the data content and actual situation, the hydrochemical items involved in the evaluation are: pH, total hardness, Cl-, F-, Cu, Pb, Zn, Cd, Co, Ni, Mn, Hg, Cr6+, As, * * * * 17.
(2) Personal evaluation results
Four typical water samples were selected from the wetland groundwater recharge area (1), runoff area (1) and drainage area (2), and the water quality of groundwater monitoring sampling points was evaluated by single component according to the above evaluation method (Table 3-9).
As can be seen from Table 3-9, the evaluation scores (Fi) of pH value, F-, Co and Cr6+ of all sampling points are all 0, and the water quality is excellent. In the total hardness evaluation score, Qixing Minjing is 3 points, which belongs to the type of good water quality, and the other points are all 0 points, and the water quality is excellent; In the Cl- evaluation score, Qixingmin well is 1, and the water quality is good, while the evaluation score of other stations is 0, and the water quality is excellent; In the content evaluation score, except for the groundwater in Qixingmin well, which has increased slightly for several months, the other evaluation scores are all 0, and the water quality is excellent; The water content of Qixingmin Well is high, with the evaluation score of 10, and the water quality is extremely poor, so it is not suitable for drinking. The groundwater evaluation index at the outlet of Shizishan underground river also reaches 1 in individual months, which needs attention. The evaluation scores of other stations are all 0, and the water quality is excellent. The groundwater content at the outlets of Qixingmin Well and Shizishan Underground River rose sharply in a few months, and the water quality became worse, making it unsuitable for drinking. The water quality at other points was excellent. The contents of Cu, Pb and Zn in groundwater at various points in the wetland are low, belonging to Class I or Class II water quality, and the water quality is good; Except for the high Cd content in the effluent of Xiaoxiangshan underground river in individual months, which belongs to Class III water quality, all other points belong to Class I or Class II water quality; The Ni content of well water in Qixingmin is high, and the evaluation score of individual months can reach 10, and the water quality is extremely poor. Other points have low content and belong to Class I or II water quality. The Mn content of groundwater in Rongtan in the northeast of Jin Quan is high, and the water quality is poor in some months, but the water quality in other points is excellent. The contents of Hg and As in the groundwater at various points in the wetland are low, mostly of Grade I and II water quality, and the water quality is excellent.
Table 3-9 Individual Evaluation and Comprehensive Evaluation Index of Groundwater Quality in Huixian Karst Wetland
(3) Comprehensive evaluation results
The comprehensive index method was used to evaluate the water quality of four groundwater monitoring sampling points in Huixian karst wetland (Table 3-9). The results show that the groundwater quality evaluation score of Huixian karst wetland is between 0.74 and 7.20, and the water quality is good or bad. Generally speaking, from groundwater recharge area to drainage area, from no man's land to residential area, F value gradually increases. The karst pool in the northeast of Jin Quan is located in the transition zone from the groundwater recharge area to the drainage area (wetland) in the north of the wetland. The comprehensive evaluation index is only 0.74, and the water quality is excellent. Qixing Minjing is located in the center of wetlands and residential areas, with a comprehensive evaluation index of 7. 17, which is higher in some months and the water quality is poor, so it is no longer suitable for residents to drink. The outlet of Shizishan underground river is also located in the groundwater discharge area of the wetland center, and the comprehensive evaluation index is higher than that of the recharge area. However, because it is an underground river system, the water exchange and groundwater velocity are relatively fast, so the value of F is relatively low compared with that of Qixingmin Well.
In addition, through the comprehensive evaluation index of Shizishan underground river outlet and Qixingmin well in different months, we can see that the difference of the former is obviously greater than that of the latter. The reasons may be as follows: the outlet of Shizishan underground river is located in the underground river system, which responds quickly to rainfall and the outlet flow changes greatly, and the ion content in it also changes with the change of water quantity, so the F value changes greatly; Qixingmin Well is located in Gu Feng Plain, with relatively gentle groundwater level and velocity, and little change in F value.
3. Analysis of organic pollution
From June/KOOC-0/0 to June/KOOC-0/7, 2007, the organic pollution of the main water bodies in the wetland (surface water, underground rivers, lakes and fish ponds) was detected and analyzed, and the water sample Q/KOOC-0/-Q9 was collected on June/KOOC-0/0, 2007. WM 1—WM8 was collected in June 65438+1October 65438+July 2007, and three samples were groundwater points, namely Q2 (exit of Eddie Underground River), WM 1 (Kamimurai) and WM5 (Seven Star Wharf). The rest are surface water bodies, including rivers, channels, lakes and fish ponds.
Organic pollution of groundwater is analyzed and evaluated according to Groundwater Quality Standard GB/T 14848- 1993, and surface water is analyzed and evaluated according to Surface Water Environmental Quality Standard GB 3838—2002. The test and analysis results (Table 3- 10) show that:
1) Most single water quality indexes of most surface water meet the national Class I water standard, and only a few indexes of individual water intake points do not meet the national standard.
2) Over-standard surface water bodies are mainly fish ponds and water bodies near villages. Among them, the unqualified BOD5 and COD are Q5 (the water in the middle of Hu Si Lake), Q9 (the water from Houtouqiao Duck Farm in Xiguanzhuang), WM7 (the door of Dulong Farm) and WM8 (the water from the north fish pond in the central hill of Dulong Farm). The unqualified COD are WM4 (lake and swamp water between Dulong and Longshan) and WM5 (Qixing Wharf water).
3) The single index of groundwater is mostly Grade III water quality, but the total coliforms and bacteria all exceed the standard.
Fish ponds, especially duck ponds, are generally poor in water quality, green in color and fast in algae reproduction. Some duck ponds sometimes even have "water bloom" phenomenon, with low conductivity (e.g. 190μs/cm in Dulong fish pond), low dissolved oxygen (e.g., 2.9mg/L in Mojia section of the western section of the ancient canal), high total Escherichia coli and cell count, and high COD and BOD5. Take Sitangsi Lake as an example. Before being polluted in 2005, the water was clean and transparent, and the water quality was good. There are many different kinds of fish and shrimp in the lake. However, since some water bodies in the upper reaches of Hu Si Lake were rented out as farms (about 60,000 ducks were raised) in the spring of 2006, the water bodies in the lake became turbid rapidly, turned black gradually, and at the same time gave off a strong fishy smell, which aggravated the degree of eutrophication. Water hyacinth in the lake proliferated rapidly from the first few trees, and by the autumn of 2006, it had covered more than half of the lake water, with a coverage rate of over 95%, resulting in extreme hypoxia and dissolved oxygen in the water. Pollutants (including dead Eichhornia crassipes) were deposited at the bottom of the lake, decomposed and rotted, resulting in high organic matter content in the water, and the thickness of sediment deposited at the bottom of the lake reached more than 1m, and the lake gradually became swampy. However, the total number of Escherichia coli and cells in groundwater exceeds the standard, which is mainly related to the pollution of surrounding surface water.
Three, wetland hydrochemical cycle-the migration and transformation of dissolved substances in water
Hydrochemical cycle is closely related to water cycle or hydrological process. In the process of wetland transformation, due to the influence of topography, geology and aquatic organisms, the hydrodynamic conditions of wetland and the physical and chemical properties of water body usually change, which leads to the migration and reorganization of chemicals in water body. Huixian wetland and its surrounding areas are typical karst areas, and the main hydrochemical action is the dissolution and precipitation (recrystallization) of carbonate rocks. In addition, the adsorption of rocks and wetland sediments and bio-ecological processes also play an important role in the transformation of hydrochemicals.
1. calcium and magnesium cycle and wetland water purification
Most of the atmospheric rainfall in the bare karst mountain areas around the wetland is transformed into karst groundwater through karst cracks, which brings minerals and debris from the surface into the ground. On the one hand, the rainwater initially entering the underground aquifer contains a large amount of liquid CO2 dissolved in the air, which combines with water to form carbonic acid and decomposes into H+ and H+. On the other hand, calcite (CaCO3) dissolves into sum in water, and then combines with H+ ions in water through hydrolysis (dolomite is similar to this, but the dissolution intensity is smaller). These two processes will lead to the increase of Ca2+, Mg2+, H+, plasma concentration and salinity in water [4]. Especially in the water-bearing medium of carbonate rock dominated by karst fractures, the contact area between water and rock is large, the flow velocity is relatively slow, the dissolution process is sufficient, and the carbonate rock is fully dissolved. If the groundwater flow rate is slow in dry season, long-term dissolution will lead to the continuous increase of ion concentration in water. Once the ion concentration in water reaches saturation, it will recombine with Ca2+ to form calcite. However, after the rest is discharged with groundwater (mainly in flood season) and brought to rivers and lakes, due to the change of hydrodynamic conditions and environment, it dissociates into sum, which combines with calcium carbonate to form calcium carbonate precipitation, resulting in the decrease of ion concentration and salinity (including hardness and salinity) in water, which is also the water purification process caused by wetland hydrochemical cycle. It is obvious in the annual rainy season wetland that karst groundwater brings a lot of minerals dissolved in dry season into the wetland every year. In the relatively static water environment in the center of wetland (such as near Longshan), a thick calcium film is formed on the leaves of submerged plants with the change of hydrochemical conditions. When the thickness of calcium film exceeds the tolerance of plant leaves, it will fall off from the leaves and deposit in the mud at the bottom of the wetland. Similarly, there are hydrolysis of silicate minerals and formation of clay minerals in wetlands. With the decrease of chemical content in water, the water itself has been purified. The water quality test of the main water bodies in Huixian Wetland shows that the contents of the main chemical components in the water bodies are obviously reduced from the upstream to the downstream of the river (underground river) or from the periphery of the wetland to the center of the wetland (Figure 3-25 ~ Figure 3-28), especially the mineral content, Ca2+, H+, total ion concentration, total hardness and total alkalinity in the water bodies, indicating that the wetland has obvious degradation effect on the chemical substances in the water bodies. However, the chemical composition of water in some testing points is mostly high, such as the ancient canal bridge in Feng Jia in the middle and lower reaches of the wetland water cycle and the four-hole bridge at the east lake exit of Qixing Wharf. The reason for this is the following：
Table 3- 10 Detection Results of Organic Pollution in Water Bodies of Huixian Karst Wetland
1) Geochemical background and groundwater recharge: From the chemical composition curve, it can be seen that the chemical composition content of karst groundwater in karst rocky mountain (carbonate rock) distribution area is generally higher than that of surface water in wetland distribution area. Feng Jia ancient bridge is located at the intersection of the ancient canal and Fengjiayan karst overflow wetland, and the recharge of karst groundwater may be the main reason for the high concentration of chemical components in the water.
2) The influence of geochemical background value in runoff area: For example, Mg2+ in wetland water increased in different degrees when it flowed through the exposed and semi-exposed areas of dolomite.
3) Influence of human activities: For chemical components with low content in water, such as trace elements and Cl-, the change of their concentration values is the most sensitive to the influence of human activities, which leads to the disorder of the spatial distribution of these chemical components in water. Among them, the high content of Cl- and Cl- in wetland water may be related to the pesticides used in wetland cultivated land and fish ponds. The change of organic matter content is related to the eutrophication of wetlands and fish ponds.
Figure 3-25 Chemical Concentration Curve of Main Water Bodies in Huixian Wetland (I)
Figure 3-26 Chemical Concentration Curve of Main Water Bodies in Huixian Wetland (II)
Figure 3-27 Chemical Concentration Curve of Main Water Bodies in Huixian Wetland (III)
2. Adsorption of rocks and minerals to purify the water quality of wetlands.
Water pollution includes toxic chemicals and organic substances. After these two pollutants enter the water body, they participate in the hydrochemical cycle of wetland. There are few industrial and mining enterprises in Huixian wetland and its surrounding areas, and the pollution sources are mainly small-scale mining (such as mining Mamian pyrite and dolomite powder in Fenghuangshan, Doumen and Sitang and Siliangshan) and chemical fertilizers and pesticides in fish ponds. Among them, pyrite with pits (Figure 3-29 and Figure 3-30) has the most obvious pollution to the surrounding areas.
Figure 3-28 Chemical Concentration Curve of Main Water Bodies in Huixian Wetland (IV)
Figure 3-29 Mamian pyrite pollution
Figure 3-30 Surface Water Pollution of Pit-surface Pyrite (Pit-surface Surrounding)
Mamian pyrite is located near Shangcun, north of Mamianwei, Huixian Town. The mine has stopped large-scale mining, but there are still small-scale mining activities. The water pollution caused by mine tailings and tailings washed by rain in rainy season (high content of Zn2+ and Mn2+ in groundwater, low pH value and poor water quality) has a great impact on the production and life of people in Shangcun-Mamian area downstream. 1999 65438+1On October 27th, Guilin Testing Station tested the water quality of the drinking well water in the village of Guangxi Urban Water Quality Monitoring Network, and the well water was yellow. 12 test items, 6 items seriously exceed the hygienic standard for drinking water GB 5749-85, and 1 item exceeds the maximum allowable concentration of harmful substances in surface water TJ. The re-inspection results of water quality at 5438+00 on September 26, 2003 and June 2007 are similar (Table 3- 1 1). In 2007, we did a comparative verification test. It can be seen that due to the large-scale mining of the mine, the pollution degree is gradually reduced with the passage of time, but the pollution is still serious in rainy season every year (the water body is yellow-red) and the sludge at the bottom of the well is still rusty yellow. Local villagers have been drinking this groundwater for a long time, and they have had many symptoms and even died; Mine tailings also cause the decline of grain yield and quality of hundreds of acres of cultivated land downstream, which poses a great threat to the production and life of local people.
However, after the mine polluted tail water enters the karst groundwater circulation, the downstream pollutant concentration gradually decreases. For example, in August 2007, the pH value of supergene karst spring flowing through mine tailings was 3.0; The pH value of polluted groundwater entering the mine living area is about 6.0, and the pH value of villagers' well water is 6.33 ~ 6.8 from downstream to upstream, and the acidity gradually weakens. At the edge of wetland, the concentration of pollutants in water is not obvious, and the pH value is above 7.0. The reason may be related to the adsorption of ions in water by rocks (minerals) and soil.
Adsorption is a common phenomenon of material exchange between solid and liquid contact surfaces. In the process of long-term contact and interaction between groundwater and stratum rocks and soil (sediments), adsorption plays an important role in controlling the formation and evolution of groundwater chemical components and the migration of solutes (especially contaminated solutes) [5]. The mechanism of adsorption is very complicated and can be summarized as physical adsorption and chemical adsorption. Physical adsorption in nature (mainly relying on surface electrostatic attraction to adsorb liquid-phase impurities) is more common than chemical adsorption, especially in Huixian wetland, where loose sediments contain a large number of clay minerals (negatively charged on the surface), which can adsorb a large number of cations in water well, thus purifying water quality. However, the water pollution in this pyrite mine area is mainly gradually purified during the migration of carbonate bedrock cracks and pipeline media, which may be related to the comprehensive adsorption of colloid and cracks on the surface of bedrock cracks and clay in underground rivers.
Table 3- 1 1 Water Quality Test Results of Dongshang Village, Mamian North, Huixian County
Fourthly, the influence of wetland bio-ecological process on soil and water geochemical cycle.
Most aquatic plants have the functions of absorbing heavy metal ions in water and soil (sludge), organic pollution, absorbing carbon dioxide in water and air, releasing oxygen and regulating climate. However, the absorptive capacity of different aquatic plants (communities) in the ecological process is quite different.
1. Relationship between aquatic plant community and dissolved oxygen in water
On April 24, 2007, the dissolved oxygen and conductivity of water in three habitats, namely, the water without aquatic plants, the water with submerged plants and the water with emergent plants, were comparatively tested in the waters near the central Longshan of Mudong Lake in Huixian wetland. The test instrument is YSI6820, and the test time is about 10h. The test results (Figure 3-3 1, Figure 3-32) show that:
Figure 3-3 1 dissolved oxygen in different plant communities in Mudong Lake
Figure 3-32 Mineralization in Water of Different Plant Communities
1) The dissolved oxygen in water is directly proportional to the water temperature, which reflects that the water temperature has a strong influence on the biological activities of aquatic plants (oxygen release) or the process of oxygen entering the water body in the air, but it lags behind in time.
2) The dissolved oxygen value in submerged plant community is the highest, followed by emergent plant community, and the dissolved oxygen value in water without aquatic plants is the lowest. The level of dissolved oxygen in water reflects the oxygen-making function of plants, but the oxygen-making function of emergent plant communities may be more reflected in supplementing oxygen in the surrounding air.
3) Floating biological communities generally grow in quasi-still water environment with slow water flow. On the one hand, their oxygen production function is mainly reflected in their contribution to the surrounding air; On the other hand, the water quality in still water environment is generally poor, which leads to a large number of plankton reproduction and covers the water surface (such as algae, water hyacinth, etc.). ), so the dissolved oxygen in water is generally low. For example, the lake south of the temple on the right bank of the Qingshui River in Sitang is completely covered by water hyacinth (also known as water hyacinth) (the coverage rate is 99%), and the dissolved oxygen in the lake is close to 0 (Table 3- 12).
Table 3- 12 Test results of water quality parameters of water hyacinth phytoplankton community (June 65438+1October 2007)
2. Relationship between aquatic plants and electrical conductivity (salinity)
The relationship between them is not obvious (Figure 3-32), especially in the emergent plant waters, like the waters without aquatic plants, the overall conductivity tends to decrease after noon, but the conductivity of submerged plant waters seems to be inversely proportional to temperature, whether it reflects the influence of temperature on biological and biochemical activities needs further observation and inspection.
3. Water purification function of several main aquatic plants (communities)
(1) floating plants and Eichhornia crassipes communities
The ability of wetland aquatic plants to absorb heavy metal ions varies greatly. Generally speaking, the ability to absorb heavy metal ions has the law of submerged plants > floating plants > emergent plants. However, some floating plants, such as Eichhornia crassipes, Spiraea, Alternanthera philoxeroides, Potamogeton crispus and so on. , has a high absorption capacity for heavy metals in water, and their large appearance also shows that the water body is in a state of eutrophication. Among them, Eichhornia crassipes is stronger than other aquatic plants in absorbing heavy metal ions and organic pollution because of its developed fibrous roots.
Eichhornia crassipes (also known as water hyacinth) is an exotic species in wetland and belongs to floating plants. It grows in slow-flowing water bodies, such as wetland lakes, lakes, fish ponds or ancient canals, especially eutrophic water bodies. Therefore, Eichhornia crassipes is also an indicator plant of eutrophication. Water hyacinths in Huixian wetland are mainly distributed in ancient canals and Miao lakes in Qingshui River basin (Figure 3-33). The width, narrowness or individual size of leaves reflect the eutrophication degree of water quality.
In order to study the ecological function of Eichhornia crassipes, in 2007, the water quality of Hu Si Lake in Sitang Township, the center of Shangyou Lake (pearl culture, open waters, no Eichhornia crassipes), the downstream lakes (photos, the coverage rate of Eichhornia crassipes is 99%), the outlet of Hu Si Lake and Qingshui River were tested. The test results (Table 3- 13) show that the water quality at the entrance of Hu Si Lake is slightly polluted, and the exposed water surface in the middle of Hu Si Lake (pearl farm and duck farm) is seriously polluted, with high organic and inorganic parameters. However, after being purified by the densely grown Eichhornia crassipes in Hunan, Hu Si, all the water quality indexes at the outlet of Hu Si Lake have been obviously improved. In particular, the organic pollution of minerals and the adsorption of heavy metals are obvious.
Figure 3-33 Eichhornia crassipes in the eastern section of the ancient canal
At the same time, the negative impact of Eichhornia crassipes on water environment is also considerable. The rapid propagation and dense distribution of Eichhornia crassipes can block rivers, block sunlight, isolate the circulation of oxygen in water, make the water lack of dissolved oxygen, and then affect the growth of submerged plants and fish, greatly reducing the biodiversity within its coverage.
Polypodiaceae is also one of the floating plants widely distributed in Huixian wetland, which generally grows from river bank to river bank. Polypodiaceae itself has no negative impact on the environment, but it provides a relatively stable breeding and supporting place for the growth and reproduction of Eichhornia crassipes.
(2) Comparison of adsorption capacity of cattail, Zizania latifolia, Sophora alopecuroides and underwater sediments for heavy metal pollution.
In order to compare the absorption capacity of different aquatic plants and underwater sediments (sludge) for heavy metals, the chemical components of the dominant aquatic plants Sophora alopecuroides (representing submerged plants), Typha Typha and Zizania latifolia (representing submerged plants) and underwater sediments (representing the growth environment of aquatic plants) widely distributed in Huixian wetland were analyzed. The results (Table 3- 14) show that:
1) The concentration of heavy metal components absorbed by aquatic plants is generally lower than that of underwater sediments where they grow, indicating that wetland sediments play a leading role in the process of water purification, and at the same time reflect the control of heavy metal components in sediments on the ion concentration of plants on them. However, there is no correlation between the concentrations of the two, and the concentrations of individual indicators (such as Cd of Vallissima) in some plants are higher than the background concentrations of corresponding indicators in sediments. It may reflect the selective absorption of certain heavy metal components (pollutants) by some plants or their biogeochemical effects (such as biomineralization). For example, cattail can absorb a lot of iron and manganese in water and sediments, and Sophora alopecuroides can not only absorb a lot of iron and manganese, but also have a preference for zinc, chromium, arsenic and niobium.
Table 3- 13 Analysis and test results of water quality parameters of phytoplankton community in water hyacinth (June 2007).
Table 3- 14 Comparison of adsorption capacity of several main aquatic plants and underwater sediments for heavy metal pollution (2007: 1 1)
2) The heavy metal components absorbed by submerged plant VALLISNERIA natans are less than those in underwater sediments, but generally several times to several times stronger than those of emergent plants (Typha latifolia and Zizania latifolia); Only a few indicators (such as Mn and Mo) are exceptions; Other submerged plant communities (such as Setaria viridis and POTAMOGETON bambusae). Similarly, it generally grows in clean, transparent and flowing water, and has no negative impact on the environment; Only the explosive growth of Kuroshio in summer and autumn will block the river, affect the growth of other submerged plants, and also have a certain negative impact on water quality.
3) The contents of iron and manganese in three aquatic plants are relatively high. Is it related to the regional background value or to the sewage discharge of Mamian pyrite in the upper reaches of the basin? Further research is needed.