The Environmental Diagnosis of Lake Worcester - Term Paper Example

Introduction Lake Worcester’s watershed covers an extensive area that is estimated to be about 4,050 hectares. The watershed is primarily used for agricultural purposes which include livestock and cash crops. Most of the land that is used for agriculture within the watershed is irrigated. However, agricultural activities seem to be reducing with time as more land in the watershed is being set aside for state and federally funded projects. Also, different agencies are continuing to lease or purchase areas which do not favor crops and turning them into wildlife areas. It is hard to trace the history of land use in relation to conversion of wetlands to tillable land. The major changes seen over the years have come from the addition of tile lines and drainage ditches through the various wetland zones which initially covered the watershed. The reclamation of approximately 350 hectare of wetland and upland area around the Huerkamp ditch is the most recent change within the watershed. The ditch together with the surrounding land was purchased by the Mid-West Department of Natural Resources (MDNR) within the 1990 summer for addition into the Mid-West State Water Bank. As a result, the ditch and the plugging of the culvert were partially filled and connected to Lake Worcester. This action subsequently got rid of one source of non-point pollution entering the lake and also created a new wetland area within the watershed (Schueler, 226) Eutrophication of the lake Basing on the 1986 surface water quality data, there only seem to be a slight improvement of water quality since then. During the monitoring period of 1990, the overturn phenomenon was experienced by the lake. This phenomenon is associated with wind action and cooling of the surface waters. As the surface water cool, it becomes denser then the wind does the mixing and this increases the amount of dissolved oxygen (DO). In the action, the available nutrients are also mixed throughout the column. During the months that little or no ice was experienced, the lake underwent thermal stratification and this resulted in lower hypolimnion having dissolved oxygen concentrations below 1mg/ l for short periods of time. The oxygen levels remained moderately constant during the ice-on months until late January when bottom parts of the lake indicated slightly reduced levels of oxygen than other parts of the water column. By February, concentrations of dissolved oxygen in the lower 5m of the hypolimnion began to reduce and the bottom 1m became anoxic. The presence of anoxia in the hypolimnion at the water-sediment boundary for a long period of time facilitates the release of phosphorus from the sediments. The index of water clarity or transparency is measured by the depth of light penetration using a Secchi disk. This can be related to the measure of trophic state as well as algal biomass of the lake. A reduction in clarity of water is due to turbidity which consists of organic matter, phytoplankton as well as suspended sediments. The range for water transparency was 0.91 – 4.28 meters and this was obtained from sampling conducted in the ice-free months only. Comparatively, the water transparency results were slightly better than those obtained in 1986. The current measurements conducted by secchi disks indicate that Lake Worcester is eutrophic. Eutrophic conditions show that there is abundance of plant nutrients as well as algae in the lake. Phosphorus is a major nutrient associated with eutrophication, a process that generally involves algal blooms, growth of vascular plants (microphytes), and reduction in transparency of water, a shift in fishery and a diminished aesthetic value. Little or no dissolved oxygen in the hypolimnion of the lake along the substrate boundary can result in the release of phosphorus that was bound by the sediments. High levels of phosphorus concentrations from anoxia are usually experienced in late summer and in early spring before ice-out. Chlorophyll-a, a photosynthetic component found in aquatic vascular plants and algae indicates the presence of algal blooms within the water column. During the monitoring season, the average chlorophyll-a concentration was 18.5 ug/l. Compared with earlier conducted tests, the current concentrations of chlorophyll are a little higher than the previous concentrations indicating greater algal biomass. Total suspended solids (TSS) in the surface water significantly affect the fishery as well as transparency of water within a water body. During the monitoring season, the total suspended solids ranged from 1.0 to 32.0 mg/l and the mean TSS was 5.9 mg/l. During this period, total suspended solids consisted of approximately 55 percent organic material and the remainder inorganic solids. Studies were conducted on Lake Worcester’s macrophytes in June and August of 1990. These studies were compared with earlier studies and there was an indication that the zonation and composition of the lake’s macrophytes have basically remained the same. The only noteworthy disparity was the expansion of the cattails around the shoreline. With enough soil and light, aquatic vegetation can generally be found to depths of about 15 feet. In the eastern segment of the lake, there is no plant growth beyond the 7-foot counter level. The western segment, on the other hand, the shallow water depth has resulted in submerged as well as emergent vegetation. Due to this, this segment of the lake serves as habitat for wildlife and fish. The algae composition in Lake Worcester during the 1990 survey consisted of 39 species. Among these were 11 genera of brown and yellow-green algae (chrysophyta) and 8 genera of green algae (Chlorophyta), 5 genera of blue-green algae (cyanophyta), 2 genera of cryptophyta and a genus of dinoflagellates (pyrrophyta). Techniques to manage Eutrophication in Lake Worcester One of the most effective ways to control algal blooms and eutrophication within the lake is by limiting nutrient supply to the lake. Chlorophyll-a and phosphorus are among the nutrients that need to be controlled. The growth of algae can be limited by light, and reduction in the concentrations of nutrients may not have a substantial effect until the nutrient concentrations are lowered enough to stimulate nutrient limitation. The sources of the nutrients must be identified first before an effective control measure can be reached. Once the possible sources of phosphorus are identified, the control techniques identified below can be for applicability and feasibility: point source management – control of point sources, especially piped discharges; Non-point source management, control of disperse nutrient sources from the watershed; hydraulic controls – flushing, dilution diversion as well as hypolimnetic withdrawal strategies; removal of bottom feeding fish – removal of major recyclers of nutrients; inactivation of phosphorus – chemical binding of phosphorus to limit availability; bacterial additives – facilitating uptake of nutrients by non-algal microbes and dredging – removal of nutrient laden deposits. The needed reduction in loading of phosphorus should be modeled to envisage the change trophic status. Generally, the problems will be reduced at loadings lower than Vollenweider’s permissible level, which is a calculated value that mainly depends on the depth as well as hydraulic residence time of the lake. The management team of Lake Worcester should be ready to adjust strategies in response to resultant lake conditions; control of algal blooms through limitation of nutrients is always an alternative process. Other methods to directly limit the abundance of algae in Lake Worcester may be needed on a supplemental or interim basis, and include the use of biocontrol agents, dyes or biocidal chemicals. However, it is not possible to control many aquatic vascular plants by nutrient reductions and direct techniques need to be applied. These direct techniques include chemical, biological and physical techniques such as biological control, dredging and sonication (use of sound waves to disrupt and kill algal cells). In the case of stubborn species, prevention is at least as vital as management of on hand infestations. The most desirable management option could be preventing the introduction of non-native plants in the lake. According to Schueler (258), one of the ways of introduction is the landscaping and aquarium trades. Watershed controls can also be used. These include enhanced storm water treatment, fertilizer restrictions, development of regional wastewater lines agricultural best management practices, riparian restoration and use of communal wastewater tanks. Along with these initiatives, is the need for strong awareness campaign to promote uptake and help limit the nutrients’ input to the lake. Conclusion Lake Worcester did not exhibit significant vertical stratifications in terms of pH temperature and dissolved oxygen but did indicate seasonal inconsistency for these and other water quality parameters. Water transparency and alkalinity reduced during peak blooms of cyanobacteria while there was an increase in concentrations of dissolved oxygen especially at the lake surface. Total phosphorus exhibited a strong positive relationship with chlorophyll-a concentrations but were inversely proportionate to dissolved phosphorus concentrations suggesting that the phytoplankton community used up some dissolved fractions of phosphorus. There are several options that can be pursued at Lake Worcester to manage the lake’s eutrophication. Each option should be carefully examined from a cost-benefit perspective and ensure that environmental impacts to lake Worcester are minimized. However, it should also be kept in mind that many options do not provide instant results, but are rather long term plans for management of nutrients. References Laws, Edward: Aquatic Pollution: An Introductory Text. New York: John Wiley and Sons: (2005) Schueler, Thomas: Microbes and Urban Watersheds: Concentrations, Sources, & Pathways: Reprinted in The Practice of Watershed Protection: 2000 Read More