Response of a Lake Michigan coastal lake to anthropogenic catchment disturbance

A paleolimnological investigation of post-European sediments in a Lake Michigan coastal lake was used to examine the response of Lower Herring Lake to anthropogenic impacts and its role as a processor of watershed inputs. We also compare the timing of this response with that of Lake Michigan to examine the role of marginal lakes as ‘early warning’ indicators of potential changes in the larger connected system and their role in buffering Lake Michigan against anthropogenic changes through biotic interactions and material trapping. Sediment geochemistry, siliceous microfossils and nutrient-related morphological changes in diatoms, identified three major trophic periods in the recent history of the lake. During deforestation and early settlement (pre-1845–1920), lake response to catchment disturbances results in localized increases in diatom abundances with minor changes in existing communities. In this early phase of disturbance, Lower Herring Lake acts as a sediment sink and a biological processor of nutrient inputs. During low-lake levels of the 1930s, the lake goes through a transitional period characterized by increased primary productivity and a major shift in diatom communities. Post-World War II (late 1940s–1989) anthropogenic disturbances push Lower Herring Lake to a new state and a permanent change in diatom community structure dominated by Cyclotella comensis . The dominance of planktonic summer diatom species associated with the deep chlorophyll maximum (DCM) is attributed to epilimnetic nutrient depletion. Declining Si:P ratios are inferred from increased sediment storage of biogenic silica and morphological changes in the silica content of Aulacoseira ambigua and Stephanodiscus niagarae . Beginning in the late 1940s, Lower Herring Lake functions as a biogeochemical processor of catchment inputs and a carbon, nutrient and silica sink. Microfossil response to increased nutrients and increased storage of biogenic silica in Lower Herring Lake and other regional embayments occur approximately 20–25 years earlier than in a nearby Lake Michigan site. Results from this study provide evidence for the role of marginal lakes and bays as nutrient buffering systems, delaying the impact of anthropogenic activities on the larger Lake Michigan system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43091/1/10933_2004_Article_1688.pd

Operation and research at the Ithaca MAP3S regional precipitation chemistry site

Annual precipitation chemistry data from network start-up through 1988 is presented for the nine MAP3S sites. Time trends show significant negative linear regressions (P < 0.10) for SO{sub 4}{sup 2-} at 2 sites, H{sup +} at 4 sites, Ca{sup ++} at 1 site, and Na{sup +} at 1 site. Significant positive regressions over time include: NH{sub 4}{sup +} at 2 sites, Ca{sup ++} at 1 site, K{sup +} at 4 sites, and Cl{sup {minus}} at 2 sites. The Ithaca site shows the highest number of significant trends, with positive trends for Cl{sup {minus}}, NH{sub 4}{sup +}, Ca{sup ++}, and K{sup +}, and a negative trend for H{sup +}. Linear regressions of annual SO{sub 4}{sup 2-} concentrations on SO2 emissions show a significant positive relationship for Whiteface, Illinois, and Ohio at p < 0.10, 0.02, and 0.05 respectively. Overall for all MAP3S sites, plus Hubbard Brook a 25% decline in SO2 emissions over the region has been accompanied by a 16.5% decline in annual precipitation concentrations of SO{sub 4}{sup 2-}. For the region as a whole, a 20% decline in combined emissions has been accompanied to a 20% decline in H{sup +} concentrations. Thus a linear relationship exists between combined emissions and precipitation H{sup +} concentrations. No strong relationship exists for NOx emissions and precipitation NO{sub 3}{sup {minus}} concentration at the annual, seasonal or monthly level. Removing the NOx transportation sector, removing high and low precipitation values, or high pH values also does little to improve the NOx -- NO{sub 3}{sup {minus}} concentration relationships. Dry deposition components such a PAN, NO2, gaseous HNO{sub 3}, or aerosol NO{sub 3}{sup {minus}} should be included in the future with precipitation NO{sub 3}{sup {minus}} to relate emissions of NOx to nitrogen deposition. 11 refs., 27 figs.,1 tab

Defining and using best available science: A policy conundrum for the management of aquatic ecosystems

Integrative research has been the dominant theme in this Special Issue, demonstrated by contemporary examples of effective collaborations and solutions for the successful engagement of scientists in the policy and management arena. Evident in these papers is the increasing use of the term 'best available science' (BAS) as a basis for well-informed resource management decisions. The term is used to engender credibility and trust among stakeholders and promotes greater awareness, communication, involvement, transparency and understanding among research, policy and management communities. However, there remains no clear statement of the properties of BAS or guidance on its practical application in the decision-making process. We define the attributes that underpin BAS and examine the issues of uncertainty, risk and communication as key challenges to successful integrative management. We advocate an interdisciplinary process that facilitates understanding of discipline-based knowledge structures, articulates uncertainty and risk about the scientific information, and promotes engagement and trust among the generators and users of information. Ultimately, successful management of aquatic ecosystems will rely on scientists, managers and decision makers who have the skills and courage to apply the best science available and not wait for the best science possible

Calcium weathering in forested soils and the effedt of different tree species

Soil weathering can be an important mechanism to neutralize acidity in forest soils. Tree species may differ in their effect on or response to soil weathering. We used soil mineral data and the natural strontium isotope ratio Sr-87/Sr-86 as a tracer to identify the effect of tree species on the Ca weathering rate. The tree species studied were sugar maple (Acer saccharum), hemlock (Tsuga Canadensis), American beech (Fagus grandifolia), red maple (Acer rubrum), white ash (Fraxinus Americana) and red oak (Quercus rubra) growing in a forest in northwestern Connecticut, USA. Three replicated sites dominated by one of the six tree species were selected. At sugar maple and hemlock sites the dominant mineral concentrations were determined at three soil depths. At each site soil, soil water and stem wood of the dominant tree species were sampled and analyzed for the Sr-87/Sr-86 ratio, total Sr and Ca content. Atmospheric deposition was collected and analyzed for the same constituents. Optical analysis showed that biotite and plagioclase concentrations were lower in the soil beneath hemlock than beneath sugar maple and suggested species effects on mineral weathering in the upper 10 cm of the mineral soil. These results could not be confirmed with data obtained by the Sr isotope study. Within the sensitivity of the Sr isotope method, we could not detect tree species effects on Ca weathering and calculated Ca weathering rates were low at all sites (<60 mg m(-2) yr(-1)). We found a positive correlation between Ca weathering and the total Ca concentration in the surface soil. These results indicate that the absolute differences in Ca weathering rate between tree species in these acidic surface soils are small and are more controlled by the soil parent material (plagioclase content) than by tree species