Nutrient Overload and Eutrophication in Freshwater Systems: Causes and Solutions

Abstract

One of the major driving factors for degradation of freshwater ecosystems worldwide has been identified as a surplus of nutrients, primarily stemming from anthropogenic input of N and P. This study aimed to investigate the underlying causes of lacustrine and riverine eutrophication and to rank the relative impact of agricultural inputs, wastewater inputs, and internal sediment nutrient loads on each system type. To assess impacts on the biodiversity, oxygen regime, and occurrence of toxic algal blooms, a two-year, multi-site high-resolution limnological monitoring program was undertaken. Total phosphorus concentrations of >0.03 mg L resulted in a critical threshold below which cyanobacteria were more likely to dominate the ecosystem due to a decrease in light penetration, creation of anoxic conditions, and shifting food web structure. The ecological implications of this critical threshold were mitigated using structural remediation (buffer zones, chemical precipitation) and biological remediation (microbial inoculation) approaches in a controlled mesocosm environment. It was found that structural techniques like chemically-bound phosphorus reduced nutrients quickly but non-sustained, whereas biological remediation, like bio-augmentation and macrophytal restoration, showed more sustained, long-term nutrient control and prevented reoccurrence of cyanobacteria. Results indicated that integrated watershed management, which combines both source reduction techniques with in-stream manipulation, can result in effective and long-lasting management of freshwater systems. The results indicate that management strategies must be applied proactively with a variety of approaches in order to ameliorate eutrophicated environments, as well as maintain the quality and functions of freshwater ecosystems currently stressed from artificial eutrophication.