Total Maximum Daily Load for Algae and Turbidity, Little Wall Lake, Hamilton County Iowa, 2005

(2005) Total Maximum Daily Load for Algae and Turbidity, Little Wall Lake, Hamilton County Iowa, 2005. Natural Resources, Department of

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Abstract

The Federal Clean Water Act requires the Iowa Department of Natural Resources (IDNR) to develop a total maximum daily load (TMDL) for waters that have been identified on the state’s 303(d) list as impaired by a pollutant. Little Wall Lake has been identified as impaired by algae and turbidity. As later explained in Section 3 of this document, the algae and turbidity impairments are symptomatic of excessive phosphorus and suspended solids loading to the lake. Phosphorus, which is related through the Trophic State Index (TSI) to chlorophyll and Secchi depth (a measurement of water clarity), is targeted to address the algae and turbidity impairments. Suspended solids, which are composed of both organic and inorganic particulate matter, are the primary transport mechanism for phosphorus. Load and wasteload allocations for suspended solids are not included in this TMDL. However, reductions in phosphorus loading should produce corresponding reductions in the suspended solids load. The purpose of the TMDL included herein is to determine the maximum allowable phosphorus load that the lake can receive and still meet water quality standards.