Impacts of Eutrophication on Water Quality and Biodiversity

Eutrophication is an ecological challenge that exhibits adverse effects on the aquatic ecosystem as well as the sustenance of portable water required by humans for their unremitting survival on the earth. Water eutrophication in lakes, reservoirs, estuaries and rivers is widespread all over the world and the severity is increasing, especially in developing countries like China. Eutrophication is the process by which water bodies, such as estuaries, coastal waters, and lakes, become enriched in dissolved nutrients, such as phosphorus and nitrogen, resulting in increased growth of algae and aquatic plants as well as the deterioration of the water’s esthetic and life-supporting qualities.[1]It occurs naturally over centuries as lakes age and are filled in with sediments. The major influencing factors on water eutrophication include nutrient enrichment, hydrodynamics, environmental factors such as temperature, salinity, carbon dioxide, element balance,  and microbial and biodiversity. Eutrophication then restricts water use for fisheries, recreation, industry, and drinking because of increased growth of undesirable algae and aquatic weeds and the oxygen shortages caused by their death and decomposition.[2]

Human activities have accelerated the rate and extent of eutrophication through both point-source discharges and non-point loading of limiting nutrients, such as nitrogen and phosphorus runoff from farmlands, effluent from aquaculture ponds as well as municipal and industrial discharge. Anthropogenic activities are the worst culprit of nutrient enrichment and the root cause of eutrophication of water bodies. Excess nutrient inputs to water bodies usually come from sewage, industrial discharges, agricultural runoff, construction sites, and urban areas. The statistical evidence on the occurrence of eutrophication in different regions of the world has been reported in some scientific findings. Further, aquaculture is the method of producing shellfish, fish and even aquatic plants without the use of soil and since it is not managed properly,  the undigested food particles combined with the fish excretion rapidly increases the level of nitrogen and phosphorous in the water which results in dense growth of microscopic floating plants and eventually causes eutrophication. Natural disasters like floods and the natural run-off of water into rivers and streams carry away excess nutrients and drain them, thus causing excessive growth of algal blooms. Similarly, when water bodies grow old, they naturally accumulate sediments and phosphorus and nitrogen nutrients which contribute to the explosive growth of bacteria like phytoplankton and cyanobacteria blooms. The coastal belt of Karachi, Pakistan was studied to estimate the nutritional levels of shallow seawater, just like it was found that the coastal regions of Port Qasim, Clifton and Hawke’s Bay Beach, when compared with the coastal regions of Ibrahim Haideri and Karachi Port Trust Kemari, are more impacted with anthropogenic contamination. The over presence of reactive nitrogen and other nutrients was the indication of disposal of solid waste, sewage effluent, and industrial effluents.[3]

Cyanobacterial blooms are amongst the stern consequences of eutrophication that cause the coating of shorelines as well as boat hulls with stinking scum resulting in odour and taste problems in water bodies, thereby rendering it unfit for desirable use due to its potential hazard to wildlife and the human populace. Eutrophication sets off a chain reaction in the ecosystem, starting with an overabundance of algae and plants. The excess algae and plant matter eventually decompose, producing large amounts of carbon dioxide. This lowers the pH of seawater, a process known as ocean acidification. Acidification slows the growth of fish and shellfish and can prevent shell formation in bivalve mollusks.[4] This leads to a reduced catch for commercial and recreational fisheries, meaning smaller harvests and more expensive seafood. Moreover, it also lessens the amount of light entering, reducing the growth of aquatic plants and causing death of plants in the depth of water bodies, which makes it difficult for the predators to catch their prey, due to which certain species become endangered as food chains are destroyed, causing death of many organisms. As algae’s growth increases, the shellfish accumulate the poison in their muscles, which acts on human bodies as well when they consume fish, it then leads to respiratory and cardiac issues in humans.[5] The routes of nutrient enrichment of the coastal belt of Karachi were identified during the research field survey. It was clear from the survey that disposal of Karachi city’s domestic waste (i.e., high in organic constituents), untreated sewage (i.e., high in ammonia, nitrates and phosphates), and disposal of untreated industrial effluent (i.e., rich in various nutrients) via Lyari river and Malir river runs to the seawater of the Karachi coastal belt causes the elevation of nutrient level of seawater.[6]

In Pakistan, laws to address and prevent eutrophication are part of a broader set of environmental protection regulations aimed at water quality management. There are several laws and regulations in place to tackle environmental issues like water pollution and eutrophication, enforcement and specific targeting of eutrophication can be somewhat fragmented. Pakistan Environmental Protection Act (PEPA), 1997  provides a legal framework for the protection, conservation, rehabilitation, and improvement of the environment in Pakistan. It empowers the Pakistan Environmental Protection Agency (Pak-EPA) to enforce laws related to environmental pollution, including water quality. These organizations and agencies have been trying to remove algae from the surface of water bodies by discharging the wastewater into rivers and streams only after proper treatment through water treatment plants, and most of the nitrates and phosphates are removed from waste material before draining it into rivers.[7] These laws and efforts have resulted in some success as the Studies conducted between 2010-2015 reported improvements in water quality. For example, phosphorus levels in Haleji Lake decreased by 40% from 2012 to 2015, which directly contributed to reduced eutrophic conditions.[8] Moreover, the national environmental quality standards have established specific ways for the wastewater discharge of effluents into water bodies. These ways are designed to reduce pollutants such as nitrogen and phosphorus that can lead to eutrophication. The standards apply to various industries, including agriculture, textile, and chemical industries.  Due to weak enforcement of laws addressing eutrophication, it is a big challenge for Pakistan because the implementation of these laws often faces resistance due to lack of resources, political will, and capacity at the local level. There is a need for more education and awareness among farmers, industries, and local governments about the harmful effects of eutrophication and the steps that can be taken to prevent it. As an individual to control eutrophication, more trees can be planted along the bed streams to slow erosion and absorb nutrients. To maintain the internal nutrient release, physical, chemical, biological techniques, and even bionic techniques could be selected.[9]

In conclusion, eutrophication remains a major environmental challenge, driven by nutrient pollution from agricultural runoff, industrial effluents, and untreated sewage. While efforts in Pakistan have led to positive outcomes, such as reduced nutrient levels in certain water bodies, the problem persists in many regions. Effective management requires stronger enforcement of environmental regulations, better wastewater treatment, sustainable agricultural practices, and increased public awareness. By continuing to invest in these solutions and enhancing cooperation between government agencies, industries, and local communities, Pakistan can work toward mitigating the impacts of eutrophication and safeguarding its precious water resources for future generations.

References:

1. Xiao-e Yang, ‘Mechanisms and Assessment of Water Eutrophication’ (March 2008) PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC2266883/.
2. Arthur J Hasler, ‘Eutrophication’ (January 2025) AccessScience https://www.accessscience.com/content/article/a247000.
3. VH Smith, ‘Eutrophication’ (2009) ScienceDirect https://www.sciencedirect.com/topics/earth-and-planetary-sciences/eutrophication.
4. Farhad Ali, ‘Impact of Eutrophication on Shallow Marine Water near Karachi Coast, Pakistan’ (Pakistan Academy of Sciences) https://www.paspk.org/wp-content/uploads/2019/02/4-B-LS-485-Impact-of-Eutrophication-on-Shallow-Marine-Water-near-Karachi-Coast-Pakistan.pdf.
5. Solomon Oluwaseun Akinnawo, ‘Eutrophication: Causes, Consequences, Physical, Chemical and Biological Techniques for Mitigation Strategies’ (August 2023) ScienceDirect https://www.sciencedirect.com/science/article/pii/S2667010023000574.
6. Soon-Jin Hwang, ‘Eutrophication and the Ecological Health Risk’ (31 August 2020) PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC7503835/.
7. Farhad Ali, ‘Impact of Eutrophication on Shallow Marine Water near Karachi Coast, Pakistan’ (Pakistan Academy of Sciences) https://www.paspk.org/wp-content/uploads/2019/02/4-B-LS-485-Impact-of-Eutrophication-on-Shallow-Marine-Water-near-Karachi-Coast-Pakistan.pdf .
8. Taj Muhammad Jahangir, Muhammad Yar Khuhawar, and Mehmood Sultan Leghari, ‘Water Quality Assessment of Haleji Lake (Sindh, Pakistan): A Ramsar Recognized Site’ (2013) Journal of the Chemical Society of Pakistan 35(3) https://www.researchgate.net/publication/282771428_Water_Quality_Assessment_of_Haleji_Lake_Sindh_Pakistan_A_Ramsar_Recognized_Site
9. Christian O Asadu et al., ‘Enhanced Efficiency Fertilizers: Overview of Production Methods, Materials Used, Nutrients Release Mechanisms, Benefits and Considerations’ (2024) Current Research in Green and Sustainable Chemistry 7, 100068 https://doi.org/10.1016/j.crgsc.2024.100068 .