Nutrient additions affecting matter turnover in forest and pasture ecosystems

Nutrient inputs into ecosystems of the tropical mountain rainforest region are projected to further increase in the next decades. To investigate whether important ecosystem services such as nutrient cycling and matter turnover in native forests and pasture ecosystems show different patterns of response, two nutrient addition experiments have been established: NUMEX in the forest and FERPAST at the pasture. Both ecosystems already responded 1.5 years after the start of nutrient application (N, P, NP, Ca). Interestingly, most nutrients remained in the respective systems. While the pasture grass was co-limited by N and P, most tree species responded to P addition. Soil microbial biomass in the forest litter layer increased after NP fertilization pointing to nutrient co-limitation. In pasture soils, microorganisms were neither limited by N nor P. The results support the hypothesis that multiple and temporally variable nutrient limitations can coexist in tropical ecosystems.

Ewaso Ngiro and Meru Ecosystems Elephant Corridors: Site 1-6

7 maps illustrating the elephant corridors in different sites of Ewaso Ngiro, Kenya.

Oxygen and indicators of stress for marine life in multi-model global warming projections

Decadal-to-century scale trends for a range of marine environmental variables in the upper mesopelagic layer (UML, 100–600 m) are investigated using results from seven Earth System Models forced by a high greenhouse gas emission scenario. The models as a class represent the observation-based distribution of oxygen (O2) and carbon dioxide (CO2), albeit major mismatches between observation-based and simulated values remain for individual models. By year 2100 all models project an increase in SST between 2 °C and 3 °C, and a decrease in the pH and in the saturation state of water with respect to calcium carbonate minerals in the UML. A decrease in the total ocean inventory of dissolved oxygen by 2% to 4% is projected by the range of models. Projected O2 changes in the UML show a complex pattern with both increasing and decreasing trends reflecting the subtle balance of different competing factors such as circulation, production, remineralization, and temperature changes. Projected changes in the total volume of hypoxic and suboxic waters remain relatively small in all models. A widespread increase of CO2 in the UML is projected. The median of the CO2 distribution between 100 and 600m shifts from 0.1–0.2 mol m−3 in year 1990 to 0.2–0.4 mol m−3 in year 2100, primarily as a result of the invasion of anthropogenic carbon from the atmosphere. The co-occurrence of changes in a range of environmental variables indicates the need to further investigate their synergistic impacts on marine ecosystems and Earth System feedbacks.

Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios

The ocean moderates anthropogenic climate change at the cost of profound alterations of its physics, chemistry, ecology, and services. Here, we evaluate and compare the risks of impacts on marine and coastal ecosystems—and the goods and services they provide—for growing cumulative carbon emissions under two contrasting emissions scenarios. The current emissions trajectory would rapidly and significantly alter many ecosystems and the associated services on which humans heavily depend. A reduced emissions scenario—consistent with the Copenhagen Accord’s goal of a global temperature increase of less than 2°C—is much more favorable to the ocean but still substantially alters important marine ecosystems and associated goods and services. The management options to address ocean impacts narrow as the ocean warms and acidifies. Consequently, any new climate regime that fails to minimize ocean impacts would be incomplete and inadequate.

Projected 21st century decrease in marine productivity: a multi-model analysis

Changes in marine net primary productivity (PP) and export of particulate organic carbon (EP) are projected over the 21st century with four global coupled carbon cycle-climate models. These include representations of marine ecosystems and the carbon cycle of different structure and complexity. All four models show a decrease in global mean PP and EP between 2 and 20% by 2100 relative to preindustrial conditions, for the SRES A2 emission scenario. Two different regimes for productivity changes are consistently identified in all models. The first chain of mechanisms is dominant in the low- and mid-latitude ocean and in the North Atlantic: reduced input of macro-nutrients into the euphotic zone related to enhanced stratification, reduced mixed layer depth, and slowed circulation causes a decrease in macro-nutrient concentrations and in PP and EP. The second regime is projected for parts of the Southern Ocean: an alleviation of light and/or temperature limitation leads to an increase in PP and EP as productivity is fueled by a sustained nutrient input. A region of disagreement among the models is the Arctic, where three models project an increase in PP while one model projects a decrease. Projected changes in seasonal and interannual variability are modest in most regions. Regional model skill metrics are proposed to generate multi-model mean fields that show an improved skill in representing observation-based estimates compared to a simple multi-model average. Model results are compared to recent productivity projections with three different algorithms, usually applied to infer net primary production from satellite observations.

Assessing the effectiveness of a long-standing rocky intertidal protected area and its contribution to the regional conservation of species, habitats and assemblages

1. The acceptance of reserves as a useful management strategy relies on evidence of their effectiveness in preserving stocks of harvested species and conserving biodiversity. A history of ad hoc decisions in terrestrial and marine protected area planning has meant that many of these areas are contributing inefficiently to conservation goals. The conservation value of existing protected areas should be assessed when planning the placement of additional areas in a reserve network. 2. This study tested (1) the effectiveness of protection for intertidal molluscs of a marine reserve (Bouddi Marine Extension, NSW, Australia) established in 1971, and (2) the contribution of the protected area to the conservation of regional species, assemblages, and habitats. 3. The shell length and population density of one harvested (Cellana tramoserica), and three non-harvested species (Bembicium nanum, Morula marginalba, Nerita atramentosa) of intertidal molluscs were examined in the protected area and two reference locations over two seasons. 4. The heavily collected limpet C. tramoserica was significantly larger in the protected area and was the only species to exhibit a significant difference. No species significantly differed in population density between the protected area and reference locations. 5. Temporally replicated surveys of macro-molluscs at 21 locations over 75km of coastline identified that the existing protected area included 50% of species, two of five assemblage types and 19 of 20 intertidal rocky shore habitats surveyed in the study region. Reservation of a further three rocky reefs would protect a large proportion of species (71%), a representative of each assemblage and all habitat types. 6. Despite originally being selected in the absence of information on regional biodiversity, the protected area is today an effective starting point for expansion to a regional network of intertidal protected areas.

Origin and evolution of reactive and noble gases dissolved in matrix pore water

Reactive and noble gases dissolved in matrix pore water of low permeable crystalline bedrock were successfully extracted and characterized for the fist time based on drillcore samples from the Olkiluoto investigation site (SW Finland). Interaction between matrix pore water and fracture groundwater occurs predominately by diffusion. Changes in the chemical and isotopic composition of gases dissolved in fracture groundwater are transmitted and preserved in the pore water. Absolute concentrations, their ratios and the stable carbon isotope signature of hydrocarbon gases dissolved in pore water give valuable indications about the evolution of these gases in the nearby-flowing fracture groundwaters. Inert noble gases dissolved in matrix pore water and their isotopes combined with their in-situ production and accumulation rates deliver information about the residence time of pore water.

Multiyear predictability of tropical marine productivity

With the emergence of decadal predictability simulations, research toward forecasting variations of the climate system now covers a large range of timescales. However, assessment of the capacity to predict natural variations of relevant biogeochemical variables like carbon fluxes, pH, or marine primary productivity remains unexplored. Among these, the net primary productivity (NPP) is of particular relevance in a forecasting perspective. Indeed, in regions like the tropical Pacific (30°N–30°S), NPP exhibits natural fluctuations at interannual to decadal timescales that have large impacts on marine ecosystems and fisheries. Here, we investigate predictions of NPP variations over the last decades (i.e., from 1997 to 2011) with an Earth system model within the tropical Pacific. Results suggest a predictive skill for NPP of 3 y, which is higher than that of sea surface temperature (1 y). We attribute the higher predictability of NPP to the poleward advection of nutrient anomalies (nitrate and iron), which sustain fluctuations in phytoplankton productivity over several years. These results open previously unidentified perspectives to the development of science-based management approaches to marine resources relying on integrated physical-biogeochemical forecasting systems.

Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation

Nitrous oxide (N2O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources. The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial–interglacial and millennial timescales. It is not well understood, however, how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations. Here we present N2O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the N2O cycle, we find a 30 per cent increase in total N2O emissions from the late glacial to the interglacial, with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation, even though there is no a priori connection between the drivers of the two sources. However, we find that terrestrial emissions dominated on centennial timescales, consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces. The results improve our understanding of the drivers of natural N2O emissions and are consistent with the idea that natural N2O emissions will probably increase in response to anthropogenic warming.