Impacts of Rotational Grazing and Riparian Buffers on Physicochemical and Biological Characteristicsof Southeastern Minnesota, USA, Streams

We assessed the relationship between riparian management and stream quality along five southeastern Minnesota streams in 1995 and 1996. Specifically, we examined the effect of rotationally and continuously grazed pastures and different types of riparian buffer strips on water chemistry, physical habitat, benthic macroinvertebrates, and fish as indicators of stream quality. We collected data at 17 sites under different combinations of grazing and riparian management, using a longitudinal design on three streams and a paired watershed design on two others. Continuous and rotational grazing were compared along one longitudinal study stream and at the paired watershed. Riparian buffer management, fenced trees (wood buffer), fenced grass, and unfenced rotationally grazed areas were the focus along the two remaining longitudinal streams. Principal components analysis (PCA) of water chemistry, physical habitat, and biotic data indicated a local management effect. The ordinations separated continuous grazing from sites with rotational grazing and sites with wood buffers from those with grass buffers or rotationally grazed areas. Fecal coliform and turbidity were consistently higher at continuously grazed than rotationally grazed sites. Percent fines in the streambed were significantly higher at sites with wood buffers than grass and rotationally grazed areas, and canopy cover was similar at sites with wood and grass buffers. Benthic macroinvertebrate metrics were significant but were not consistent across grazing and riparian buffer management types. Fish density and abundance were related to riparian buffer type, rather than grazing practices. Our study has potentially important implications for stream restoration programs in the midwestern United States. Our comparisons suggest further consideration and study of a combination of grass and wood riparian buffer strips as midwestern stream management options, rather than universally installing wood buffers in every instance. RID=" ID=" The Unit is jointly sponsored by the US Geological Survey, Biological Resources Division; the Minnesota Department of Natural Resources; the University of Minnesota; and the Wildlife Management Institute.     

Profiles and removal efficiency of polycyclic aromatic hydrocarbons by two different types of sewage treatment plants in Hong Kong

Sewage discharge could be a major source of polycyclic aromatic hydrocarbons(PAHs) in the coastal waters. Stonecutters Island and Shatin Sewage Treatment Works(SCISTW and STSTW)in Hong Kong, adopted chemically enhanced primary treatment and biological treatment,respectively. This study aimed at(1) determining the removal efficiencies of PAHs,(2) comparing the capabilities in removing PAHs, and(3) characterizing the profile of each individual PAHs, in the two sewage treatment plants(STPs). Quantification of 16 PAHs was conducted by a Gas Chromatography. The concentrations of total PAHs decreased gradually along the treatment processes(from 301 ± 255 and 307 ± 217 ng/L to 14.9 ± 12.1 and 63.3 ± 54.1 ng/L in STSTW and SCISTW, respectively). It was noted that STSTW was more capable in removing total PAHs than SCISTW with average total removal efficiency 94.4% ± 4.12% vs. 79.2% ± 7.48%(p 0.05). The removal of PAHs was probably due to sorption in particular matter, confirmed by the higher distribution coefficient of individual and total PAHs in solid samples(dewatered sludge contained92.5% and 74.7% of total PAHs in SCISTW and STSTW, respectively) than liquid samples(final effluent-total contained 7.53% and 25.3% of total PAHs in STSTW and SCISTW, respectively).Despite the impressive capability of STSTW and SCISTW in removing PAHs, there was still a considerable amount of total PAHs(1.85 and 39.3 kg/year, respectively for the two STPs) being discharged into Hong Kong coastal waters, which would be an environmental concern.