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Habitat Assessment

Nutrient Loadings

Aerial view of an algal bloom on the River Rouge. Photo: The Rouge River Project

Nutrients - in particular nitrogen and phosphorous - occur naturally in the environment and are essential building blocks for plant and animal growth. Excessive nutrient loading, however, can result in the accelerated growth of macrophytes or phytoplankton, potentially harmful algal blooms that lead to oxygen declines, imbalance of aquatic species, public health threats and a general decline in the aquatic resource. Nutrients are discharged into waterways from various point and non-point sources. The primary sources of nutrients are nonpoint, and include agricultural runoff, eroded soils, urban stormwater runoff and wastewater runoff. Potential point sources include quarries, mines and industrial and municipal discharges. Research has shown that the key factors that cause eutrophication - or over-enrichment - of waterbodies are excessive concentrations of the primary nutrients phosphorus and nitrogen .

A primary source of excess nutrients is agriculture. While proper application of nutrients produces healthy crops, inmproper use and a lack of buffers can contribute to water quality problems in lakes and streams. Another concern is the increasing trend toward larger animal production facilities, known as Concentrated Animal Feeding Operations (CAFOs). Traditionally, manure, litter, and wastewater produced at an animal feeding operation are applied to cropland as fertilizer. The growing number of CAFOs and the increased amount of agricultural waste has resulted in nutrients that exceed crop needs. It is unclear to what extent CAFO waste contributes to water quality degradation and research is needed to document its impacts.

Urban areas discharge nutrients to the environment as well. Excessive use of fertilizers is a major source of nutrients from golf courses and urban homeowners. Urban homeowners can typically apply many times the amount of fertilizer needed to support their lawns or gardens. The excess fertilizer runs off the property, flows into sewer systems and accelerates plant growth downstream. Natural wetlands can remove some nutrients from storm water runoff but development has reduced these natural filtration areas, increasing the nutrient loads to the region's habitat.

Other urban nonpoint sources include combined sewer overflows (CSOs), sanitary sewer overflows (SSOs), failing onsite sewage disposal systems (OSDSs, also known as septic systems) and discharge from municipal and industrial wastewater treatment plants, which can all contribute excess nutrients to the region's water bodies. While the primary concern regarding these sources is bacteria loadings that impact human health, they can also impact the health of the aquatic communities in the study area.

For more information, see: Coastal Habitat Plan, Section V (PDF)