Algal Growth Response in Two Illinois Rivers Receiving Sewage Effluent

Phosphorus (P) primarily enters streams in Illinois as effluent released from sewage treatment plants and runoff from agricultural fields. As a result, water quality can be affected and large amounts of algal growth are possible. We determined the growth of periphytic algae (as chla) relative to differing amounts of P (factor of 10) released in sewage effluent in two rivers. The Salt Fork Vermilion River and the Copper Slough branch of the Kaskaskia River both have a sewage treatment plant near their sources. Periphytic algal growth was assayed in each river with unglazed ceramic tiles (five week period) at 10 sites, each 10 km apart downstream from where the treatment plant was located. Field measurements included canopy cover, turbidity, water depth (to the tile surface), and water temperature. The concentrations of sestonic algae (as chla), total P, dissolved reactive P, nitrate-N, dissolved organic carbon, and Si were determined in water samples. Total P concentrations were different between the two rivers, ranging from 1.9 mg L just below the Salt Fork Vermilion River plant to 0.67 mg L 90 km downstream; corresponding values were 0.19 and 0.16 mg L for the Kaskaskia River. Phosphorus concentrations were not related to sestonic or tile periphytic chla in either river. Canopy cover, turbidity, and unstable sediments apparently regulated algal growth by limiting the penetration of light. Therefore, P was not the primary regulator of algal growth, and removing sewage effluent P from these rivers is unlikely to alter algal growth. INTRODUCTION The growth of algae in rivers in Illinois is controlled by various factors such as nutrient concentrations, turbidity, and light (Figueroa-Nieves et al. 2006). Although each of these factors can regulate algal production, phosphorus (P) has been thought to have a critically important effect on algal growth (Van Nieuwenhuyse and Jones 1996, Dodds et al. 1998). In Illinois, P is added to streams from both sewage effluent and agricultural runoff (David and Gentry 2000, Gentry et al. 2007). The increase in P and other nutrients to rivers has been thought to cause environmental degradation because it decreases the quality of the water and can cause eutrophication. As a result, there can be an increase in algal blooms, which can be toxic to other organisms. Eutrophication can result in large fish kills because the amount of oxygen in the water at night is reduced as a result of the large algal blooms (Morgan et al. 2006). Loss of biodiversity is also a consequence because many organisms are lost that cannot tolerate these conditions. Nutrient enrichment, particularly for P in fresh waters, is commonly listed as a primary impairment in midwestern rivers (USEPA 2000). States are currently under federal pressure to develop nutrient criteria (Dodds and Welch 2000, USEPA 2007) that would be likely to include concentration standards for nitrogen (N) and P in streams and rivers. If standards are put into place, one of the first regulated sources is likely to be sewage effluent, primarily because it is a permitted source with technology available to reduce both nutrients. However, it is not clear for many midwestern rivers if sewage effluent N and P were greatly reduced (even to zero) that stream quality would improve ____________________ Corresponding author: [email protected]