TMDL development for the Taihu Lake’s influent rivers, China using variable daily load expressions

Abstract

Influent river carrying nutrient pollutants from watershed loads makes a great contribution to the eutrophication in river-fed lake. It is scientific standard to make policies on river pollution control based on loading capacity of the river of interest. To control eutrophication in Taihu Lake has been the focal point of “The Twelfth Five-Year Guideline” proposed by Chinese government. The Taigeyunhe, Caoqiaohe and Yincungang Rivers which were the most polluted influent rivers in Taihu Lake Basin were scheduled for nutrient total maximum daily load (TMDL). A variety of mechanistic and empirical models are applied worldwide for TMDL development. However, model selection depends on management objectives, site-specific characteristics and availability of data resource. In this study, based on watershed characteristics and limited data, a nutrient TMDL is developed using flow and temporally variable daily load expressions. The simple and effective approaches specify allowable daily maximum loads for controlling on instantaneous high load and allowable daily median loads for achieving long-term TMDL allocation. For the entire river system, loading capacities are much lower during low flows. The maximum percent load reductions for biochemical oxygen demand, ammonia nitrogen, total nitrogen in spring and total phosphorus in winter can be obtained when pollution source inputs seasonally vary. This study provides local authority with two different alternatives in decision-making for pollution control on influent rivers and then to reduce external loads to the lake.