Slope length effects on microbial biomass and activity of eroded sediments

Abstract

Due to climatic and topographic conditions, soil erosion is a major problem in Turkey; approximately 86% of the land is suffering from some degree of erosion. This study investigated the relationship between bare soil slope length and the erosion-induced degradation of soil quality and the loss of carbon (C) and nitrogen (N) from the microbial biomass in eroded sediment in the Western Black Sea Region of Turkey. Six erosion study plots were constructed at an altitude of 146 m with a mean slope of 30%. Each plot had a width of 1.87 m and two slope lengths (5.5 and 11.0 m) with the long axis oriented downslope. Runoff and sediments were collected in two tanks arranged in series at the base of each plot. Microbial biomass carbon (C (mic)) and nitrogen (N (mic)) were estimated using the chloroform-fumigation extraction method. Moreover, basal respiration was determined by quantifying the carbon dioxide (CO(2)) released in the process of microbial respiration during 7 days of incubation. Data from six field runoff plots with two slope lengths (5.5 and 11.0 m) revealed that short slopes had more runoff per unit area than long slopes. In contrast, the total soil loss per unit area increased with increasing slope length. The estimated total annual losses of microbial C and N were 641.72 and 106.90 g ha(-1) year(-1), respectively, for short slopes and 814.32 and 153.46 g ha(-1) year(-1), respectively, for long slopes. Microbial communities of eroded sediment in long slopes are energetically more efficient (lower qCO(2)) with correspondingly higher C (mic)/C (org) ratios (increased biomass) compared to short slopes. The present study demonstrated that increased soil loss results in increased C (mic)/C (org) percentages and decreased qCO(2). Moreover, the eroded sediment from long slopes exhibited a healthier eco-physiological profile compared to sediment from short slopes.