Ecological Assessment of Riparian Buffer Strip Effectiveness in Reducing Agricultural Runoff in Anambra State

Agricultural runoff laden with sediment, nutrients, and pesticides is a primary driver of freshwater degradation in South East Nigeria. Riparian buffer strips represent a widely promoted best management practice for intercepting pollutants before they reach stream channels. This study assessed the effectiveness of existing and newly established riparian buffer strips in reducing agricultural runoff impacts on streams in three local government areas of Anambra State. Paired catchment designs were used to compare water quality at streams with and without effective riparian buffer strips under identical land use conditions. Water quality monitoring during rainfall events captured event mean concentrations of total suspended solids, nitrate, phosphate, and selected pesticides at each paired site. Vegetation structure and ground cover of buffer strips were measured to characterise buffer quality. Results showed that intact multi-species buffer strips of 20 metres or wider reduced total suspended solid event loads by 65 to 78 percent compared to unprotected reaches. Nitrate and phosphate reductions were more variable, averaging 42 and 35 percent respectively. Degraded or narrow buffer strips of less than 10 metres provided minimal pollution interception. The study recommends formalising riparian buffer strip requirements of at least 20 metres in Anambra State agricultural extension guidelines and incorporating buffer strip mapping into routine land use monitoring programmes. Keywords: riparian buffer, agricultural runoff, water quality, Anambra State, best management practice.