Jeffrey A. Simmons

Forest floor carbon pools and fluxes along a regional climate gradient in Maine, USA

Global carbon (C) reserves in soil are large compared with atmospheric stocks (in the form of CO2 and methane), so small changes in soil C storage will have a significant effect on atmospheric CO2 concentrations. In order to better understand the consequences of global climate change, it is essential that we define how soil C storage is influenced by changes in temperature and moisture that are expected as a result of global climate change. Forest floor carbon pools and fluxes were evaluated at 16 northern hardwood sites located within four distinct climate regions (Northern, Central, Southern and Coastal) in Maine. Mean annual air temperature at the sites ranged from 2.0°C in the Northern region to 6.2°C in the Coastal region and average annual precipitation ranged from 90 cm in the Northern region to 140 cm in the Coastal region. Leaf litter mass and leaf litter C flux were not correlated with temperature indices and did not vary among regions. However, they were positively correlated with annual precipitation, suggesting that litter production was controlled, in part at least, by precipitation but not by temperature. Northern sites stored more C in the forest floor than Coastal sites, and they experienced slower decomposition rates. Because soil and vegetation characteristics of these sites were similar, we attribute these trends to differences in climate. Indeed, C turnover time was correlated with latitude and temperature indices. Slower decomposition in the Northern region was attributed to a combination of lower specific activity at temperatures below 13°C, cooler average temperatures and a shorter frost-free season. Soil respiration at each site was positively correlated with temperature and the slope of the relationship increased with latitude, indicating that the ability of the soil biota to respire C varied with climate. A predictive equation is presented that accounts for the change in slope with latitude. Because C loss through soil respiration was more sensitive to temperature than C inputs from litter, any regional warming in the next century may lead to a decrease in forest floor carbon storage. However, if precipitation increases with temperature, then litter C flux may increase and offset the increase in soil respiration.

Indices of forest floor nitrogen status along a climate gradient in Maine, USA

Abstract Nitrogen has long been recognized as the most commonly limiting nutrient for plant production throughout the world. Yet, air pollution has created a modern chemical climate that has sometimes resulted in excess ecosystem N due to N deposition. In addition, climate warming could accelerate N cycling and N export from forested ecosystems. The result is increasing interest in understanding forest ecosystem N dynamics. This study used recently delineated climatic regions in Maine to investigate the possible influences of forest species composition, and energy and moisture gradients, on laboratory indices of forest floor N cycling. Concentrations of N and C, and potential net nitrification, potential net ammonification, and potential net N mineralization, were measured on forest floor samples from 20 sites distributed across Maine in both hardwood and softwood stands. Both forest types had nearly identical concentrations of N in the forest floor (∼1.6%), but the mean C/N ratio (28) under softwoods was significantly higher than that under hardwoods (24) due to higher concentrations of total C in soils under conifers. Forest floor N concentration was a better predictor of potential net N mineralization than was total C or C/N ratio. Although the most northerly region in this study was predictably the coldest, it was also the region with the highest values for total N and N cycling indices. Wet N deposition for the region indicates N deposition differences are not responsible for this spatial pattern, and further work is warranted to explain these results. Laboratory incubation measures of potential net N mineralization were significantly correlated with in situ annual net N mineralization, which supports the use of these techniques for forest soil N status evaluations. Most site measures of mean temperatures were negatively correlated with soil N indices indicating that warmer sites had lower rates of N cycling. Although differences existed in forest floor N characteristics between climate regions, they could not be predicted by simple relationships with temperature.

Methane fluxes in a northern hardwood forest ecosystem in relation to acid precipitation

Abstract Methane fluxes were measured periodically in 1990 and 1991 in upland forest and peatland soils of a northern hardwood forest in the Adirondack region of New York State. A portion of the study area received lime (10 Mg CaCO3 ha-1) in October 1989 to mitigate several decades of chronic acid precipitation (H+ deposition in 1981 = 653 eq ha−1 yr−1). Consumption of atmospheric methane by forest soils averaged −0.60 mg CH4 m−2 d−1 and showed no difference between treatments (unlimed versus limed soils). Eliminating root growth and removing leaf litter from the soil seemed to decrease rates of methane consumption. Related responses of soil nitrogen transformations to the lime indicated lower nitrification rates and higher net nitrogen mineralization rates compared to unlimed soils, yet rates of methane consumption were unaffected by these changes in soil nitrogen transformations. Methane efflux from the peatland soils into the atmosphere averaged 12.1 mg CH4 m−2 d−1, with no significant difference in rates between treatments. Laboratory measurements revealed that liming resulted in less consumption of atmospheric methane (measured with atmospheres amended with methane) and potentially more methane production. Overall, methane efflux from these peatland soils is much lower than that for more northern counterparts that currently experience cooler climate but less acid precipitation. This suggests that several decades of acid precipitation may play a role in limiting methane emissions from northern peatlands.

Treated and Untreated Acid Mine Drainage Effects on Stream Periphyton Biomass, Leaf Decomposition, and Macroinvertebrate Diversity

ABSTRACT We studied the effects of acid mine drainage (AMD) on three key stream properties and functions. Four streams from each of three categories (AMD, treated AMD, and reference) were selected randomly from within the Tygart Valley River watershed in West Virginia. Analysis of stream water verified that the three stream types had very distinct chemical characteristics. Periphyton biomass was significantly reduced in AMD streams; however, treated AMD streams were no different from reference streams. Leaf decomposition was significantly slower in treated streams than in reference streams. Compared to reference streams AMD streams exhibited significantly lower macroinvertebrate density and diversity, whereas treated AMD streams had lower diversity. Thus, although treated AMD is much less toxic than raw AMD, it still has substantial impacts on macroinvertebrate diversity and leaf decomposition which could lead to ecosystem-wide impacts.

Toxicity of major cations and anions (Na+, K+, Ca2+, Cl−, and SO) to a macrophyte and an alga

In many freshwater systems around the world, the concentrations of major ions (Na(+), K(+), Ca(2+), Mg(2+), Cl(-), HCO(3)(-), CO(3)(2-), and SO(4)(2-)) are exhibiting increasing trends, approaching the concentrations historically found mainly in estuaries. The objectives of the present study were to determine at what concentrations these salts are toxic to an aquatic plant and a green alga, to investigate two potential mechanisms of toxicity, and to determine the usefulness of conductivity as an indicator of salt toxicity. In a series of laboratory trials, Lemna minor and Pseudokirchneriella subcapitata were exposed to a range of concentrations of five different salts. Conductivity levels that caused 10 or 50% reductions in growth-related traits (EC10 and EC50, respectively) were determined, using conductivity of the test solutions as the independent variable. The EC10 values ranged from 0.44 to 2.67 mS/cm for P. subcapitata and from 1.3 to >19 mS/cm for L. minor. The EC50 values ranged from 1.7 to 5.8 mS/cm for P. subcapitata and from 4.2 to >27 mS/cm for L. minor. For both species the EC values varied dramatically among the salts. Pseudokirchneriella subcapitata was most sensitive to KCl and NaCl, whereas L. minor was most sensitive to Na(2)SO(4). The mechanism of toxicity does not appear to be related to production of reactive oxygen species, nor to reduction in chlorophyll concentrations. Because toxicity was strongly influenced by salt composition, regulation and management of specific ions may be preferable to conductivity.

Moving to open access

I am delighted to announce that the Journal of Freshwater Ecology will embark on a new journey in 2017 as a fully open access journal. This means that the research published in the Journal will be available for anyone to read anywhere, at any time providing they have an internet connection. This decision was not made lightly but was based on current trends in the marketplace. Funding agencies and governments more and more are requiring that the results from projects they fund be made openly available and they often provide the funds to cover the article publication charges. At the same time, library budgets for subscriptions are being reduced at a global scale. This makes it harder for paper journals, especially smaller ones, to exist under the subscription model. Open access journals are growing in number and popularity, and I and the editorial team at Taylor and Francis are confident that the journal will have a more secure future as an open access journal compared with continuing to rely on subscriptions. Two important benefits are faster publication time and greater availability to a wider readership. For our readers, authors and reviewers, the only noticeable change will be the conversion to online only publication of articles. The Journal of Freshwater Ecology will still carefully peer review all submitted papers as before. It will retain rigorous quality control such that only meaningful and important new results are accepted for publication. Becoming an open access journal will mean that Journal of Freshwater Ecology will see strong growth in usage and therefore potential citations, and greater public impact as the journal will be available for a much wider audience. The article publishing charge for Journal of Freshwater Ecology is now £470/

Methane and carbon dioxide dynamics in a northern hardwood ecosystem

750/€625 which is comparable to a longer paper at our previous page charge rate and is in line with current funding and other journals in the field. I am excited that we are taking this major step forward to ensure the long-term viability of this well-respected journal.