. 2016. Approaches to stream solute load estimation for solutes with varying dynamics from five diverse small watersheds. Ecosphere 7(6):e01298. 10. 1002/ecs2.1298 Abstract. Estimating streamwater solute loads is a central objective of many water-quality monitoring and research studies, as loads are used to compare with atmospheric inputs, to infer biogeochemical processes, and to assess whether water quality is improving or degrading. In this study, we evaluate loads and associated errors to determine the best load estimation technique among three methods (a period-weighted approach, the regression-model method, and the composite method) based on a solute's concentration dynamics and sampling frequency. We evaluated a broad range of varying concentration dynamics with stream flow and season using four dissolved solutes (sulfate, silica, nitrate, and dissolved organic carbon) at five diverse small watersheds (Sleepers River Research Watershed, VT; Hubbard Brook Experimental Forest, NH; Biscuit Brook Watershed, NY; Panola Mountain Research Watershed, GA; and Río Mameyes Watershed, PR) with fairly high-frequency sampling during a 10-to 11-yr period. Data sets with three different sampling frequencies were derived from the full data set at each site (weekly plus storm/snowmelt events, weekly, and monthly) and errors in loads were assessed for the study period, annually, and monthly. For solutes that had a moderate to strong concentration-discharge relation, the composite method performed best, unless the autocorrelation of the model residuals was <0.2, in which case the regression-model method was most appropriate. For solutes that had a nonexistent or weak concentration-discharge relation (model R 2 < about 0.3), the period-weighted approach was most appropriate. The lowest errors in loads were achieved for solutes with the strongest concentration-discharge relations. Sample and regression model diagnostics could be used to approximate overall accuracies and annual precisions. For the period-weighed approach, errors were lower when the variance in concentrations was lower, the degree of autocorrelation in the concentrations was higher, and sampling frequency was higher. The period-weighted approach was most sensitive to sampling frequency. For the regression-model and composite methods, errors were lower when the variance in model residuals was lower. For the composite method, errors were lower when the autocorrelation in the residuals was higher. Guidelines to determine the best load estimation method based on solute concentration-discharge dynamics and diagnostics are presented, and should be applicable to other studies.
Biochar has been used for soil improvement in agriculture; however, there are few studies of its uses in forestry. The purpose of this study was to investigate the effects of biochar, made from diverse feedstocks on the growth and chlorophyll content of Zelkova serrata seedlings, to identify optimal feedstocks in a containerized seedling production. Five resources were used for biochar: woodchips of Pinus densiflora and Quercus acutissima; cones of Pinus koraiensis; rice husks; and crab shells. The biochar was mixed with growing medium by 20% in volume and two levels of fertilization were applied. The height and root collar diameter of Z. serrata treated with wood chips of P. densiflora and Q. acutissima and rice husk were each significantly greater than those treated with pine cones and crab shells. The biomass responses and quality indexes were similar to those of height and root collar diameter. There were no significant differences in growth between fertilization levels. This study shows that biochar made from woodchips of P. densiflora and Q. acutissima and rice husk can be substituted for growing medium by 20% in a containerized seedling production system.
Plant nutrient acquisition in forests requires respiration by roots and mycorrhizae. Belowground carbon allocation and soil respiration should thus reflect plant effort allocated to nutrient uptake, for example in conditions of different nutrient availabilities controlled by site quality or stand history. Soil respiration, belowground C allocation, and fine root biomass were measured in three sites differing in nutrient availability in the northern hardwood forests of the White Mountains of New Hampshire. Annual soil respiration and belowground C allocation measured in two stands at each site were lowest at Jeffers Brook, the site with highest nutrient availability, and higher at Hubbard Brook and Bartlett Experimental Forests. Neither soil respiration nor belowground C allocation differed significantly between mid-aged (31-41 year old) and older stands (>80 year old) within the sites, despite higher fine root (<1 mm) biomass in old stands than mid-aged stands. During the growing season, soil respiration was low where net nitrogen mineralization and net nitrification were high across an extensive sample of thirteen stands and annual belowground C allocation decreased with increasing nitrification across the six intensively studied stands. Available P was not related to soil respiration. The relationships among N availability, belowground C allocation, and soil respiration support the claim that forests allocate more C belowground in ecosystems with low availability of a limiting nutrient.
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