Overlapping anthropogenic effects on hydrologic and seasonal trends in DOC in a surface water dependent water utility.

Drinking water supplies are increasingly affected by overlapping anthropogenic global change processes. As a key currency of ecosystem function in aquatic ecosystems, dissolved organic carbon (DOC) concentration and composition is sensitive to many global change processes. However, DOC must also be removed to avoid the production of harmful disinfection byproducts as water is processed. Thus, understanding the effects of global change processes on the seasonal and long-term dynamics of DOC composition and concentration is critical for ensuring the sustainability of drinking water supplies. To understand these dynamics, we analyzed a novel 11-year time series of stream water DOC concentration and composition using Weighted Regressions on Time Discharge and Season (WRTDS) to understand the influences of co-occurring changes in climate and atmospheric deposition. We also discuss the implications for water supply provision and management. We found that, during our study period, overlapping global change processes in the watershed had the net effect of increasing the DOC aromaticity, as measured by SUVA254, at moderate to high discharge levels during the late spring and early summer and the autumn and early winter. However, changes in DOC concentration were more dynamic and we observed both increasing and decreasing trends depending on season and hydrologic state. During summer, at low to moderate flow levels we observed a significant (p < 0.05) increase in DOC concentration. During autumn, at moderate to high flow levels we observed a significant (p < 0.05) decrease in DOC concentration and an increase in SUVA254. For drinking water providers, our results suggest that close monitoring of source waters must be coupled with the development of plans accounting for season- and hydrology-specific long-term changes.

Calcium and aluminum cycling in a temperate broadleaved deciduous forest of the eastern USA: relative impacts of tree species, canopy state, and flux type.

Ca/Al molar ratios are commonly used to assess the extent of aluminum stress in forests. This is among the first studies to quantify Ca/Al molar ratios for stemflow. Ca/Al molar ratios in bulk precipitation, throughfall, stemflow, litter leachate, near-trunk soil solution, and soil water were quantified for a deciduous forest in northeastern MD, USA. Data were collected over a 3-year period. The Ca/Al molar ratios in this study were above the threshold for aluminum stress (<1). Fagus grandifolia Ehrh. (American beech) had a median annual stemflow Ca/Al molar ratio of 15.7, with the leafed and leafless values of 12.4 and 19.2, respectively. The corresponding Ca/Al molar ratios for Liriodendron tulipifera L. (yellow poplar) were 11.9 at the annual time scale and 11.9 and 13.6 for leafed and leafless periods, respectively. Bayesian statistical analysis showed no significant effect of canopy state (leafed, leafless) on Ca/Al molar ratios. DOC was consistently an important predictor of calcium, aluminum, and Ca/Al ratios. pH was occasionally an important predictor of calcium and aluminum concentrations, but was not a good predictor of Ca/Al ratio in any of the best-fit models (of >500 examined). This study supplies new data on Ca/Al molar ratios for stemflow from two common deciduous tree species. Future work should examine Ca/Al molar ratios in stemflow of other species and examine both inorganic and organic aluminum species to better gauge the potential for, and understand the dynamics of, aluminum toxicity in the proximal area around tree boles.

The effects of phenoseason and storm characteristics on throughfall solute washoff and leaching dynamics from a temperate deciduous forest canopy.

Seasonal variations in the washoff and leaching dynamics of throughfall ionic fluxes represent a significant process affecting the biogeochemical cycling of forested ecosystems-particularly for temperate deciduous forests with distinct phenological seasons (or "phenoseasons"). Most studies on temperate deciduous forests aggregate seasonal throughfall fluxes to the leafed (growing) and leafless (dormant) periods, yet the phenological conditions controlling seasonality demand finer-scale demarcations that include the transitional phenoseasons (leaf senescence and emergence). To fill these gaps our study examines the washoff and leaching dynamics of Na(+), Mg(2+), K(+), Ca(2+), Cl(-), SO(4)(2-), and NO(3)(-) throughfall derived from bulk and sequentially sampled rain events across leafed, leafless and both transitional phenoseasons over a 3-year period (2008-2010). As throughfall washoff and leached solute fluxes are also closely-coupled to rainfall conditions, we further examine the effects of storm characteristics on phenoseasonal washoff-dominated (Na(+) and Cl(-)) and leaching-dominated (K(+), Ca(2+), Mg(2+)) fluxes through intrastorm event comparison plots and factorial MANOVA. Highly significant differences in leached and washoff solute fluxes were found across meteorological conditions (p<0.001) nested within phenoseasonal divisions (p<0.00001). Phenoseasonal washoff Na(+) and Cl(-) fluxes seemed to be more closely related to leaf area; whereas, leaching flux and canopy exchange of all solutes to correspond more with major phenological changes (when the canopies tend to be most metabolically active). The greatest differences in leached Mg(2+), K(+), Ca(2+), and SO(4)(2-) fluxes were not between the full leafed and leafless phenoseasons (33-80% difference), but between the transitional periods (80 to 200 fold greater during leaf senescence than leaf emergence). Intrastorm average canopy NO(3)(-) leaching, however, ranged from low losses (1 µmol(c)m(-2)h(-1)) to canopy uptake (-2 µmol(c)m(-2)h(-1)) during both transitional phenoseasons. K(+), Ca(2+), Mg(2+) were all markedly more exchangeable during senescence, with Ca(2+) and Mg(2+) being more tightly held by the canopy. Leaching rates and fluxes for all measured solutes were negligible to negative during emergence, except for K(+) and SO(4)(2-). Our results indicate that much of the variance in timing and magnitude of throughfall solute fluxes to forest soils within temperate deciduous ecosystems may be ascribed to phenologically-delineated seasons and storm conditions.

Sulfate exports from multiple catchments in a glaciated forested watershed in western New York, USA.

Sulfate (SO4(2-)) concentrations and fluxes were studied for multiple storm events in the Point Peter Brook watershed, a glaciated, forested watershed located in Western New York, USA. Investigations were performed across one large (696 ha) and three small (1.6-3.4 ha) catchments with varying extent of riparian and wetland areas. Concentrations of SO4(2-) in groundwater sources (mean values: 238-910 micromol(c) L(-1)) were considerably greater than concentrations recorded for rainfall (60 micromol(c) L(-1)) and throughfall (72-129 micromol(c) L(-1)). Seasonality in SO4(2-) concentrations was most pronounced for valley-bottom riparian waters with maximum concentrations in late winter-spring (February-March) and a minimum in late summer (August). Concentrations of SO4(2-) in wetland water were considerably less than riparian water indicating the likelihood of SO4(2-) reduction in anoxic wetland conditions. Storm events displayed a dilution pattern in SO4(2-) concentrations with a minimum coinciding with the maximum in throughfall contributions. End member mixing analysis (EMMA) was able to predict the storm event concentrations of SO4(2-) for four of the six comparisons. Concentrations of SO4(2-) at the outlet of the large (696 ha) catchment were much greater than values recorded for the smaller catchments. Exports of SO4(2-) in streamflow exceeded the inputs from atmospheric deposition suggesting that watersheds like Point Peter Brook may not show any immediate response to decreases in atmospheric SO4(2-) deposition.