Abstract: Assessment of both water quality and quantity pose a great challenge to those studying the effects of anthropogenic activities on bodies of water. Eutrophication created by the increased concentration of nutrients including nitrates and phosphates has been known to contribute to the development of both toxic algal blooms, which serve as limiting factors in the ecosystems of the water, rendering it useless for consumption.1,2 Another common development is the buildup of suspended sediments (SS/TSS), contributing to the anoxic conditions characterizing environmental hypoxia.3 Because current methods for the assessment of the presence of such issues rely upon tedious and costly methods, a timely and cost-efficient method is desirable for application to the practice.4 This research relies upon analysis of the inherent optical properties of chlorophyll and sedimentation present within the bodies of water in question, achieved through analysis of the reflectance values of the red and blue bands from Landsat satellite images of five bodies of water. 5 The analysis, performed using Geographic Information System ArcMap, allows for determination of the values that attest to changes in surface area, turbidity, and eutrophication. The trends in the data hold consistency with the natural occurrences surrounding the bodies of water associated with the three parameters outlined above, supporting usage of remote sensing for qualitative and quantitative analysis of water.
Introduction: Lakes are popular hosts of environmental problems as a result of anthropogenic activities. For the majority of these lakes, causes of these problems often involve sediment loading or nutrient enrichment, also known as eutrophication.1 Eutrophication is also the cause of algal bloom in water. Both eutrophication and algal bloom are a natural phenomenon, but human activities may accelerate them, which can cause harm in terrestrial ecosystems. In fact, eutrophication and harmful algal blooms are the leading source of impairment of water quality in many lakes around the world.2 Specifically, human-derived sources due to industrialization, urbanization, or agricultural wastes due to the amount of excess nutrient that these sources then load onto their local freshwater bodies. Anthropogenic activities change the amount of Nitrogen and Phosphate - both of which are nutrients essential to algal growth - present in water. For instance, sewage, agricultural, and household discharges often contain large quantities of P minerals.3 Harmful algal blooms may cause anoxic conditions, which is the depletion of oxygen in water. Such conditions are especially dominated by cyanobacteria, which is a blue alga that produces cyanotoxins and makes lake water toxic, causing wildlife deaths and seafood poisoning in humans.4
Traditional methods to measure water quality parameters like algal blooms involves field surveying techniques while measuring suspended solids involves the filtration technique.Unlike the other methods, studies show that satellite remote sensing is more cost-effective, economic, and ideal for acquiring spatial data from lakes with large surface areas7 like the ones that will be investigated. For the purpose of this study, there are two other water quality parameters measured, besides the quantity factor with surface area. One is the chlorophyll, which will indicate the severity of algal bloom, and the other is total suspended solids, as a measure of water turbidity. The Inherent Optical Property (IOP) - which refers to absorption and scattering properties of underwater contents - of chlorophyll and suspended solids were used to determine algal and sediment presence. And because of the optical properties of chlorophyll and suspended solids in water, one can use commercially available optical instruments to measure their respective concentrations.7 This can be applied to satellite data because of the way in which satellite sensors collects the intensity of light reflected. And since satellites measure reflectance values in different intervals of the electromagnetic spectrum, the focus will be placed on reflectance values on certain intervals - also known as band values - in this paper. In summary, a lower reflectance value of blue band correlates to a higher concentration of sediments. As a lower reflectance value of the red band would suggest a higher presence of chlorophyll.
In this study, two lakes across the world are analyzed, and each is chosen for the significance of their impact on local livelihood. The five lakes investigated are Lake Kasumigaura of Japan and Lake Maggiore of Europe.
References
[1] Smith, V., Tilman, G., & Nekola, J. (1999). Eutrophication: Impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental Pollution,100( 1-3), 179-196. doi:10.1016/s0269-7491(99)00091-3 12
[2] Chislock, M.F.; Doster, E.; Zitomer, R.A.; Wilson, A.E. (2013)."Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems". Nature Education Knowledge. 4 (4): 10. Retrieved 10 March 2018.
[3] Anderson, D. M., Glibert, P. M., & Burkholder, J. M. (2002). “Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences.” Estuaries,25(4), 704-726. doi:10.1007/bf02804901