Using GIS and remote sensing techniques for the identification, remediation, and protection of lakes undergoing cultural eutrophication

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1 Cameron Morissette NRS 509 Using GIS and remote sensing techniques for the identification, remediation, and protection of lakes undergoing cultural eutrophication Eutrophication is defined as an excessive richness of nutrients within a lake that causes dense plant growth and death of animal life from lack of oxygen. The driving force behind lake eutrophication is typically runoff from land. Cultural eutrophication is a term coined to describe eutrophication that is a result of human intervention within the sensitive natural lacustrine catchments, and is usually a result of increased runoff due to growing impervious surface areas and/or increased erosion and nutrient loading in proximity to agricultural regions. The overall health of a lacustrine system is adversely effected by nutrient loading and eutrophication, and it is for this reason that runoff be accurately quantified so that steps can be taken to improve the quality of natural water bodies. In the past decade, a significant interest has been on monitoring watershed runoff values in a variety of landscapes and land use classifications by using GIS technologies and remote sensing capabilities. The following is a review of recent literature (past decade) that shows the various methods that are available to researchers and policymakers so that runoff can be precisely measured, and the problem of cultural eutrophication be properly approached. The most fundamental approach to attacking the cultural eutrophication (which will be referred to as simply eutrophication for the remainder of this paper) problem is to first off determine the quality of the lake in question. Brezonik et al. (2002) developed a clear procedure and methodology to determine lake quality at the regional scale by using satellite imagery and GIS technology. Because the most expensive component of environmental remediation tends to be human labor, the value of this paper and its proposed procedure is immense because it greatly reduces the cost of pre intervention consultation. Although the GISbased runoff prediction model proposed by these researchers only provides a modest correlation factor, the water quality procedure could still be employed as a first step regional need identifier, and the immense availability of satellite imagery in the United States should only compound the interest of local and state government decision makers. Once potential problem lakes are determined, the next logical step in monitoring nutrient loads would be to monitor bulk runoff into these catchments. There is a vast amount of literature focused on quantifying runoff with GIS models. However, within the past decade there has been a large push for determining runoff in various land use areas, many of which rely on digital elevation models (DEMs) (Turcotte et al. 2001; Lufafa et al. 2003) in GIS as a basis for watershed delineation, regional slope characteristics, and basin morphology. Turcotte et al. (2001) changed the way in which GIS end users mapped watershed drainage structures by

2 improving the then popular, eight flow direction matrix (D8) method. This method could not take lake information into account due to internal limitations. The Turcotte et al. approach involves the use of a digital river and lake network (DRLN), which is not limited by the presence of lakes. This approach would no doubt be very useful for researchers interested in a specific lake within a larger drainage network. Unfortunately, it isn t only the amount of runoff that can potentially cause eutrophication, but also the type of runoff; or, specifically, the chemistry of the runoff. Eutrophication results from an excess of nutrients into a lake or water body, but the typical problem nutrients are phosphorous and nitrogen, as loading of these cause increased plant growth. Hiscock et al. (2003) were able to create a phosphorous budget and relate the values to specific land uses within the northern Okeechobee watershed in Florida. The ability to observe and tie specific loads based on surrounding environment is a huge tool for researchers and policymakers at both local and regional scales. Land use changes are obviously critical catalysts in runoff changes, as urban growth increases impervious surface coverage and, in turn, increases nitrogen laden sewage runoff, or as agricultural clear cutting leads to increased erosion of nutrient laden soils. Melesse and Shih (2002) used remote sensing and a GIS to track land use changes and the respective runoff response of the area. This study is relevant to eutrophication because it took into account not only runoff volume throughout these changes, but also differentiated soil types, and therefore runoff chemistry. Lufafa et al. (2003) provided a basis for soil erosion prediction within a microcatchment of the Lake Victoria watershed. This ability to accurately predict erosion based on soil type could be integral in determining acceptable crop types near eutrophication endangered lakes. An interesting aside to the runoff related nutrient transport into lakes is another big contributor of the hydrologic cycle: groundwater recharge. Quantifying groundwater flow into lakes has been notoriously difficult for researchers in the past, due to the challenges involved in finding inflow sources beneath a lake surface and also the cost of making in situ measurements. However, Zacharias et al. (2003) developed a clever way of using GIS technologies to estimate groundwater recharge within Lake Trichonis in Greece. By developing a digital terrain model of the lake and plugging in all relevant hydrologic data (rainfall, artificial inflow, runoff inflow, respective outflows, etc.) they were able to come up with an acceptable estimate of groundwater from a hydrologic water balance budget. Although this approach requires a significant amount of geologic and meteorologic data and also extensive field data, the ability to quantify groundwater is another way to measure possible sources of nutrients into a lacustrine system. It is obvious that the use of GIS technologies and remote sensing techniques can greatly advance our understanding of natural Earth systems, as well as in countless other disciplines outside the scope of this paper. A number of talented researchers are constantly working to not only understand our environment, but also our role in the shaping of it and various ways in

3 which we can improve it. Cultural eutrophication is a serious threat to lake biota and overall health, and the use of GIS has proven to be a cost effective and accurate approach to identifying and solving this problem. With increased interest and research, policymakers in the future will be able to make decisions based on reliable GIS and remote sensing interpretations so that we can, as a population, remediate and protect our natural environments.

4 Annotated Bibliography Brezonik, P.L., S.M. Kloiber, L. Olmanson, M. Bauer Satellite and GIS tools to assess lake quality. University of Minnesota Water Resources Center Technical report 145. Brezonik et al. provides a well written and easy to follow technical report on the quantification of lake clarity through remote sensing and GIS methods. The report not only worked towards developing techniques for using Landsat imagery on a regional scale to assess trophic conditions in lakes, but also the develop detailed procedures on the methods so that they may be carried out on a routine basis. They were also able to apply these methods to determine lake quality of the study area in previous decades. This accomplishment alone was worth the effort. By measuring total reflectance via satellite imagery, Brezonik et al. were able to determine lake clarity and compare it to field observations acquired through the classic Secchi disk method. They also were able to use a GIS system to model point source pollution and the effects of season and land use on concentrations and loads. A huge strength of this report was simply the development of a procedural system that can be carried out by any researcher (and an Appendix is given of all publications derived from the procedure). Also, the use of satellite remote sensing greatly cuts down on field measurements, which would normally be very costly to accomplish within this regional (~500 lakes) area. A major weakness lays in the GIS based runoff model, which yielded R2values of 0.78 at best. While the remote sensing methods are great for regional and site specific areas, the GIS model should only be used for non detailed regional estimates. Hiscock, J.G., C.S. Thourot, Zhang, J Phosphorous budget land use relationships for the northern Lake Okeechobee watershed, Florida. Ecological Engineering 21: Hiscock et al. used GIS methods to provide a much needed quantification of phosphorous loading related eutrophication of Lake Okeechobee, FL,. They classified the many surrounding basins using GIS soil and land use databases, and even updated the aging land use database through satellite imagery analysis. They were able to relate phosphorous loads with respective land use, soil, rainfall and runoff, and basin. The most obvious strength in this study is the ability to quantify P loads for each land cover and land use type within the Lake Okeechobee basin, and to incorporate these concentrations into a net Phosphorous budget for the entire lake. Without the GIS technology, a net P budget would have been very difficult to determine for such a large lake basin with such variable land use surroundings. The only critique I have is in regard to heavy use of math intensive regression analysis, which made the paper difficult to read in some cases. Lufafa, A., M.M. Tenywa, M. Isabirye, M.J.G. Majaliwa, P.L. Woomer Prediction of soil

5 erosion in a Lake Victoria basin catchment using a GIS based Universal Soil Loss model. Agricultural Systems 76: Lufafa et al. conducted a very interesting study of differential soil erosion for a microcatchment in the Lake Victoria Basin using a Universal Soil Loss model within a GIS platform. This type of study is relevant for the area, which is very important agriculturally, supporting over 6 million people. The model was a relatively simple erosion calculation based on the variables: rain erosivity, soil erodibility, slope steepness and length, and land cover and management practices; and was particularly useful for the study area (Uganda) where field observations are not easy to accomplish. These variables were calculated almost entirely within the GIS platform using aerial photography, DEM data, and a few other advanced statistical and GIS based skills. The main strengths of this study were the near absence of field measurements, the use of GIS GRID spatial display, which afforded the ability to apply the model to individual cells (micro areas), and also the ability to predict soil loss over large areas due to the interpolation abilities. The only weakness I find is actually within the model, which admittedly only estimates values for the input variables and would probably need more analysis for better accuracy. Melesse, A.M., S.F. Shih Spatially distributed storm runoff depth estimation using Landsat images and GIS. Computer and Electronics in Agriculture 37: Melesse and Shih used a variety of remote sensing platforms in concert with a GIS system to determine runoff curve numbers for a basin within the Kissimmee River watershed in south Florida. The US Department of Agriculture, Natural Resources Conservation Service Curve Number (USDA NRCS CN) method was used, which determines a curve number from hydrologic soil group, land use, land treatment, and hydrologic conditions data. This study was conducted with a strong use of satellite remote sensing platforms, and it was showed that these technologies were very useful for determining runoff response. Although the spatial resolution differed between platforms through time, each method still produced valid numbers. Melesse and Shih showed that these types of runoff related studies are much more accurate, convenient, and cheap with the use of satellite data within a GIS based model versus more conventional methods. Also, studies can be carried out more frequently, which is a valuable attribute for studying natural areas that change on sub annual scales. Turcotte, R., J.P. Fortin, A.N. Rousseau, S. Massicotte, J.P. Villeneuve Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network. The Journal of Hydrology. 240: Turcotte et al. significantly altered the conventional GIS methods for developing a watershed drainage structure by using a digital river and lake network (DRLN) as an input along with the digital elevation model. The conventional method involved using an eight flow direction matrix

6 (D8), but the DRLN approach has shown to be an improvement over this method. The DRLN will prove to be a much more accurate addition to hydrologic models of the future. The DRLN approach is deeply rooted within the D8 method, but does not share the same limitations. The D8 method was limited mainly by the presence of flat areas, and also could not hold information about lakes or even wide areas of river flow because the upstream area of a cell could not be split between neighboring cells. This is especially impressive when viewed side by side as in Figure 8, where the D8 method limitations are illustrated and the DRLN solution proposed. The only aspect lacking in this paper is testing of the DRLN with remote sensing data. Also, while the proposed method is a significant improvement, the D8 method is still needed and employed in many cells that are not in proximity to the DRLN. Zacharias, I., E. Dimitriou, T. Koussouris Estimating groundwater discharge into a lake through underwater springs by using GIS technologies, Environmental Geology 44: Zacharias et al. developed a water balance model to determine monthly groundwater recharge values for deep lakes a calculation that can be very difficult for hydrologists to determine in deep lakes. This feat was accomplished by using Theissen polygons to quantify rainfall into the catchment, in concert with the development of a Digital Terrain Model (DTM) from Greek military topographic maps. The DTM was used to determine change in lake storage, a key variable in any hydrologic budget. This study uses cutting edge technology to solve groundwater recharge problems that have historically been very difficult to answer. A major strength in this model is the author s obvious knowledge of geologic features, which he used many times to determine groundwater flow rates. Also, the ability to quantify groundwater recharge in such a cost efficient way is a huge strength. An unfortunate downside is the inability to check, statistically, whether or not this method is indeed more accurate than a more hands on approach. A similar study was done using in situ field observations prior to Zacharias et al., and the results differ significantly. Also, a slight downfall is that significant geologic and meteorologic field observations are needed for the model to run, which cuts down on the potential universal use of the Zacharias et al. method.