James Johnson

The potential of integrated constructed wetlands (ICWs) to enhance macroinvertebrate diversity in agricultural landscapes

Integrated Constructed Wetlands (ICWs) constitute an alternative option for the treatment of agricultural wastewater in Ireland. These surface flow systems are formed by interconnected ponds and have the capacity to fit into the landscape and provide habitat for a wide range of biota, including macroinvertebrates that have enormous potential for biodiversity enhancement. For these reasons, five ICW systems were studied. In addition, five natural ponds were investigated to account for the potential of ICW ponds to mimic natural conditions. Nine river sites were also investigated to allow for an evaluation of the catchment biodiversity contribution of the ICW systems. The present study revealed that the last ponds in the chain of these ICW systems are capable of supporting a similar number of taxa as natural ponds. Furthermore, the contribution of the last ponds to the macroinvertebrate diversity at the catchment level was high. ICWs seem to integrate their effluent management and purifying properties with that of biodiversity enhancement and landscape fit. This is the first study to investigate the potential of constructed interconnected ponds, used for wastewater treatment, to enhance biodiversity in agricultural landscapes.

Contrasting responses of two Sitka spruce forest plots in Ireland to reductions in sulphur emissions: results of 20 years of monitoring

Long-term trends in ion concentrations of bulk precipitation, throughfall, forest floor leachate (humus water) and shallow and deep soil water were assessed at two Sitka spruce (Picea sitchensis) stands—one on an Atlantic peat bog in the west of Ireland (Cloosh), the other on the east coast on a peaty podzol (Roundwood). Deposition at Cloosh was dominated by marine ions (sodium, [Na+], chloride [Cl−], and magnesium [Mg2+]), whereas bulk precipitation and throughfall at Roundwood was characterized by inputs of non-marine sulphate (nmSO42−), acidity and inorganic nitrogen (NH4+, NO3−). Significant declines in concentrations of nmSO42− and acidity in bulk precipitation and throughfall were observed at both sites. The decline in throughfall nmSO42− was significantly related to reductions in European sulphur dioxide (SO2) emissions. At Roundwood, SO42− declined significantly in humus, shallow and deep soil water. In deep soil water this was accompanied by a long-term increase in pH and a reduction in total aluminum (Altot). The recovery from acidification was delayed by high concentrations of NO3−, which strongly influenced acidity and Altot concentrations. At Cloosh, there was a significant decline in SO42− in humus water but long-term trends were not evident in shallow or deep soil water; SO42− concentrations at these depths fluctuated in response to drought-events. Marine ions strongly influenced soil water chemistry at both sites; at Cloosh soil water acidity was strongly related to Na+ and Cl−, while at Roundwood, Na+, Cl− and Mg2+ influenced Altot concentrations. Dissolved organic carbon increased significantly in humus and soil water at Roundwood, where it was associated with declining acidity. Soil water at both sites was influenced by a combination of anthropogenic sulphur (S) and nitrogen (N) deposition, drought and sea-salt events. The study highlights the value of long-term monitoring in assessing the response of forest soils to S and N deposition against a background of climate influences on soil water through drought and sea-salt events.

Quantifying Carbon and Nutrient Input From Litterfall in European Forests Using Field Observations and Modeling

Litterfall is a major, yet poorly studied, process within forest ecosystems globally. It is important for carbon dynamics, edaphic communities, and maintaining site fertility. Reliable information on the carbon and nutrient input from litterfall, provided by litter traps, is relevant to a wide audience including policymakers and soil scientists. We used litterfall observations of 320 plots from the pan-European forest monitoring network of the “International Co-operative Programme on Assessment and Monitoring of AirPollution Effects on Forests” to quantify litterfallfluxes. Eight litterfall models were evaluated (four using climate information and four using biomass abundance). We scaled up our results to the total European forestarea and quantified the contribution of litterfall to the forest carbon cycle using net primary production aggregated by bioregions (north, central, and south) and by forest types (conifers and broadleaves). The 1,604 analyzed annual litterfall observations indicated an average carbon input of 224 g C · m2· year 1 (annual nutrient inputs 4.49 g N, 0.32 g P, and 1.05 g K · m2), representing a substantial percentage of net primary production from 36% in north Europe to 32% in central Europe. The annual turnover of carbon and nutrient in broadleaf canopies was larger than for conifers. The evaluated models provide large-scale litterfall predictions with a bias less than 10%. Each year litterfall in European forests transfers 351 Tg C, 8.2 Tg N,0.6 Tg P, and 1.9 Tg K to the forestfloor. The performance of litterfall models may be improved by including foliage biomass and proxies for forest management.

Critical loads and nitrogen availability under deposition and harvest scenarios for conifer forests in Ireland

In this study we calculated the critical load of nutrient nitrogen (N) for Irish forest plots (n=380) under two harvesting scenarios: conventional stem-only harvest (SOH) and stem plus branch harvest (SBH) and two deposition scenarios: current and with a 10% increase in reduced-N. In addition, current N status was assessed using the following data from forest monitoring plots: forest floor C:N, foliar N and plant root simulation (PRS™) probe N supply rate. Average critical loads were 15.3 kg N ha(-1)year(-1) under SOH and 19.5 kg N ha(-1)year(-1) under SBH. Average total (wet+dry) N deposition was 18 kg N ha(-1)year(-1), ranging from 8.6 to 26 kg Nha(-1)year(-1). As a result, critical loads were exceeded at 67% of sites under SOH and 40% of sites under SBH. However, there was little evidence of exceedance at monitored plots. Foliar and forest floor C:N data indicated that most of these sites had low to intermediate N status. There were considerable differences in N cycling between soil types. Plant root simulation (PRS™) probe data indicated that this was likely due to differences in net N-mineralization and nitrification. Our results indicate that many sites are currently N limited but critical load exceedance suggests that these systems will accumulate N over time. The findings have implications for forest management, allowing for the assessment of nutrient management under different harvest scenarios.

The response of soil solution chemistry in European forests to decreasing acid deposition

Acid deposition arising from sulphur (S) and nitrogen (N) emissions from fossil fuel combustion and agriculture has contributed to the acidification of terrestrial ecosystems in many regions globally. However, in Europe and North America, S deposition has greatly decreased in recent decades due to emissions controls. In this study, we assessed the response of soil solution chemistry in mineral horizons of European forests to these changes. Trends in pH, acid neutralizing capacity (ANC), major ions, total aluminium (Altot ) and dissolved organic carbon were determined for the period 1995-2012. Plots with at least 10xa0years of observations from the ICP Forests monitoring network were used. Trends were assessed for the upper mineral soil (10-20xa0cm, 104 plots) and subsoil (40-80xa0cm, 162 plots). There was a large decrease in the concentration of sulphate (SO42-) in soil solution; over a 10-year period (2000-2010), SO42- decreased by 52% at 10-20xa0cm and 40% at 40-80xa0cm. Nitrate was unchanged at 10-20xa0cm but decreased at 40-80xa0cm. The decrease in acid anions was accompanied by a large and significant decrease in the concentration of the nutrient base cations: calcium, magnesium and potassium (Bcxa0=xa0Ca2+ xa0+xa0Mg2+ xa0+xa0K+ ) and Altot over the entire dataset. The response of soil solution acidity was nonuniform. At 10-20xa0cm, ANC increased in acid-sensitive soils (base saturation ≤10%) indicating a recovery, but ANC decreased in soils with base saturation >10%. At 40-80xa0cm, ANC remained unchanged in acid-sensitive soils (base saturation ≤20%, pHCaCl2xa0≤xa04.5) and decreased in better-buffered soils (base saturation >20%, pHCaCl2xa0>xa04.5). In addition, the molar ratio of Bc to Altot either did not change or decreased. The results suggest a long-time lag between emission abatement and changes in soil solution acidity and underline the importance of long-term monitoring in evaluating ecosystem response to decreases in deposition.

Responses of forest ecosystems in Europe to decreasing nitrogen deposition

Average nitrogen (N) deposition across Europe has declined since the 1990s. This resulted in decreased N inputs to forest ecosystems especially in Central and Western Europe where deposition levels are highest. While the impact of atmospheric N deposition on forests has been receiving much attention for decades, ecosystem responses to the decline in N inputs received less attention. Here, we review observational studies reporting on trends in a number of indicators: soil acidification and eutrophication, understory vegetation, tree nutrition (foliar element concentrations) as well as tree vitality and growth in response to decreasing N deposition across Europe. Ecosystem responses varied with limited decrease in soil solution nitrate concentrations and potentially also foliar N concentrations. There was no large-scale response in understory vegetation, tree growth, or vitality. Experimental studies support the observation of a more distinct reaction of soil solution and foliar element concentrations to changes in N supply compared to the three other parameters. According to the most likely scenarios, further decrease of N deposition will be limited. We hypothesize that this expected decline will not cause major responses of the parameters analysed in this study. Instead, future changes might be more strongly controlled by the development of N pools accumulated within forest soils, affected by climate change and forest management.