Eimers, M. Catherine

Although stormwater management ponds (SWMPs) are frequently used to mitigate flooding in urban areas, we still do not fully understand how these systems impact water quality in a watershed. Currently, most research focuses on the effectiveness of SWMPs to retain nutrients during high flows, even though there is potential for internal nutrient releases to occur in these systems during low flows. To investigate if SWMPs act as nutrient sources or sinks during low flow conditions, we analyzed how sewershed characteristics, pond properties, and hydrological and limnological factors influenced nutrient dynamics and stoichiometry in 10 SWMPs. Our study ponds were located in Peterborough, Whitby, and Richmond Hill, which are urbanized municipalities in southern Ontario, Canada. During October 2010 to 2011, we took monthly measurements of various carbon (C), nitrogen (N), and phosphorus (P) forms. We collected samples in the inlets, permanent pools, and outlets to determine any changes in concentrations, loads, and stoichiometric ratios into and out of the ponds. At the time of sampling, we also measured a variety of hydrological and limnological parameters. Our findings indicate that more urbanized sewersheds with higher drainage densities tend to have higher inflowing particulate and dissolved nutrient loads. In addition, we found that pond properties such as depth, length-to-width ratio, volume, and age differentially influence the retention of particulate and dissolved C, N, and P forms. Influential hydrological and limnological factors were antecedent moisture conditions, season, and thermal stratification. We found higher particulate P concentrations near the sediments when the catchments were drier and the ponds were ice-free and stratified. As well, we found higher outflowing stoichiometric ratios for DOC:TDN and DOC:TDP. This indicates an enrichment of C compared to N and P and suggests biogeochemical processes may be occurring in SWMPs. Overall, our results demonstrate that SWMPs are complex aquatic systems, and we need to consider biogeochemical processes in our design and maintenance activities, so that the effectiveness of SWMPs is not compromised during low flow conditions as a result of internal nutrient releases.

Author Keywords: Carbon, Nitrogen, Phosphorus, Urban biogeochemical cycling, Urban stormwater pond

Recovery of forest soils from chronic acidification can be enhanced with the use of non-industrial wood ash (NIWA). Non-industrial wood ash is alkaline and contains high concentrations of macronutrients, but trace metal concentrations must be evaluated to limit risk of metal toxicity following application. Additionally, understanding how different forest ecosystem components respond to NIWA is essential to inform current policy regulating its use as a soil amendment. This study evaluated the response of sugar maple (Acer saccharum) sap yield and chemistry, the response of soils beneath maple, American beech (Fagus grandifolia) and mixed species canopies, and maple and beech fine roots, foliage, seedling abundance, and understory vegetation abundance and composition to an application of 6 Mg ha-1 NIWA. Eight 40 x 40 m plots were established in a hardwood stand in Bracebridge, Ontario and were sampled prior-to and up to two years following application of NIWA (n = 4). Non-industrial wood ash significantly increased organic horizon soil pH and macronutrient (Ca, Mg, and K) concentrations with increases in Mg and K extending to the mineral soils. Significantly higher concentrations of some trace metals (Al, Fe, Mn, Cd, Cu, Pb, Zn) were also observed, but these were restricted to the organic horizons. Sugar maple sap, pH, and sweetness were unaffected by NIWA application, and while increases were observed in nutrient and metal concentrations in sap, the differences were small and variable between years, and all concentrations were consistent with those commonly found in maple sap. Fine root biomass of maple and beech trees was not affected by NIWA application, but higher concentrations of K and Mg were observed in the roots of both species, consistent with higher concentrations observed in the mineral soil horizons beneath both species' canopies. Only significant increases were observed in K in sugar maple foliage. Both critical foliar concentrations and diagnosis and recommendation integrated system (DRIS) norms for sugar maple did not indicate mineral nutrient deficiencies at this site; although this site was acidic and nutrient-poor, this may account for the lack of differences observed, particularly between species. Changes observed in understory vegetation were driven by years rather than between treatments. These results suggest that moderate doses of NIWA can provide significant decreases in soil acidity and increase nutrient availability, with limited increases in metal concentrations that are primarily restricted to the organic horizons.

Author Keywords: American beech, metal toxicity, Non-industrial wood ash (NIWA), sap sweetness, sap yield, sugar maple

Soil and tree chemistry were measured across 15 limed sites that were established 14 to 37 years ago within the Sudbury barrens in Ontario, along with two unlimed pre-treatment condition reference sites and an unlimed remnant pine forest. Soil pH and base cation (calcium (Ca), magnesium (Mg), and potassium (K)) concentrations were elevated in surface organic [FH] horizons up to 37-years post limestone treatment. Limestone in the organic horizon was evident by higher Ca/Sr ratios (a good marker of dolomite) in younger sites. Base cation mass budgets were generally unable to account for the mass of added Ca and Mg. Sudbury is characterized by widespread metal contamination. Metal (copper (Cu), nickel (Ni), and lead (Pb)) concentrations were generally greatest within the FH horizon and unrelated to stand age. Copper and Ni concentrations in soil generally decreased with distance from the nearest smelter. Metal partitioning (Kd) in soil was most influenced by soil pH rather than organic matter suggesting that as liming effects fade over time metal availability may increase.

Author Keywords: Afforestation, Degraded, Limestone, nutrient, Space-for-time, Sudbury