In northern forests, large amounts of missing N that dominate N balances at scales ranging from small watersheds to large regional drainage basins may be related to N-gas production by soil microbes. We measured denitrification rates in forest soils in northeastern North America along a N deposition gradient to determine whether N-gas fluxes were a significant fate for atmospheric N inputs and whether denitrification rates were correlated with N availability, soil O2 status, or forest type. We quantified N2 and N2O fluxes in the laboratory with an intact-core method and monitored soil O2, temperature and moisture in three forests differing in natural and anthropogenic N enrichment: Turkey Lakes Watershed, Ontario; Hubbard Brook Experimental Forest, New Hampshire; and Bear Brook Watershed, Maine (fertilized and reference plots in hardwood and softwood stands). Total N-gas flux estimates ranged from <1 in fertilized hardwood uplands at Bear Brook to >100 kg N ha(-1) year(-1) in hardwood wetlands at Turkey Lakes. N-gas flux increased systematically with natural N enrichment from soils with high nitrification rates (Bear Brook < Hubbard Brook < Turkey Lakes) but did not increase in the site where N fertilizer has been added since 1989 (Bear Brook). Our results show that denitrification is an important and underestimated term (1-24% of atmospheric N inputs) in N budgets of upland forests in northeastern North America, but it does not appear to be an important sink for elevated anthropogenic atmospheric N deposition in this region.

Topography influences hydrological processes that in turn affect biogeochemical export to surface water on forested landscapes. The differences in long-term average annual dissolved organic carbon (DOC), organic and inorganic nitrogen [NO 3 À -N, dissolved organic nitrogen (DON)], and phosphorus (total dissolved phosphorus, TDP) export from catchments in the Algoma Highlands of Ontario, Canada, with similar climate, geology, forest and soil were established. Topographic indicators were designed to represent topographically regulated hydrological processes that influence nutrient export, including (1) hydrological storage potential (i.e. effects of topographic flats/depressions on water storage) and (2) hydrological flushing potential (i.e. effects of topographic slopes on potential for variable source area to expand and tap into previously untapped areas). Variations in NO 3 À -N export among catchments could be explained by indicators representing both hydrological flushing potential (91%, p < 0.001) and hydrological storage potential (65%, p < 0.001), suggesting the importance of hydrological flushing in regulating NO 3 À -N export as well as surface saturated areas in intercepting NO 3 À -N-loaded runoff. In contrast, hydrological storage potential explained the majority of variations among catchments in DON (69%, p < 0.001), DOC (94%, p < 0.001) and TDP (82%, p < 0.001) export. The lower explanatory power of DON (about 15% less) compared with that of DOC and TDP suggests another mechanism influencing N export, such as controls related to alternative fates of nitrogen (e.g. as gas). This study shows that simple topographic indicators can be used to track nutrient sources, sinks and their transport and export to surface water from catchments on forest landscapes.

Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land-cover types and subwatersheds contributing run-off to the sampling sites in the River Njoro. Standard Digital Elevation Model-based routines were used to establish the watershed area contributing run-off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land-use types and the size of the subwatersheds. The mid-stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large-scale farming with intense, well-preserved riparian and in-stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small-scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid-reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land-use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near-stream land uses. We suggest that conser vation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem.

Climate change and climate-driven feedbacks on catchment hydrology and biogeochemistry have the potential to alter the aquatic versus atmospheric fate of nitrogen (N) in forests. This study investigated the hypothesis that during the forest growth season, topography redistributes water and water-soluble precursors (i.e., dissolved organic carbon and nitrate) for the formation of gaseous N species. Soil nitrous oxide (N 2 O) and nitrogen (N 2 ) efflux and soil physical and chemical properties were measured in a temperate forest in Central Ontario, Canada from 2005 to 2010. Hotspots and hot moments of soil N 2 O and N 2 efflux were observed in topographic positions that accumulate precipitation, which likely triggered the formation of redox conditions and in turn intercepted the conversion of nitrate N flowing to the stream by transforming it to N 2 O and N 2 . There was a strong relationship between precipitation and N 2 O efflux (y = 0.44x 1.22 , r 2 = 0.618, p < 0.001 in the inner wetland; y = 1.30x 1.16 r 2 = 0.72, p < 0.001 in the outer wetland) and significantly different N 2 :N 2 O ratios in different areas of the wetland (19.6 in the inner wetland and 10.1 in the outer wetland). Soil N 2 O + N 2 efflux in response to precipitation events accounted for 16.1% of the annual N input. A consequence of the higher frequency of extreme precipitation events predicted under climate change scenarios is the shift from an aquatic to atmospheric fate for N, resulting in a significant forest N efflux. This in turn creates feedbacks for even warmer conditions due to increased effluxes of potent greenhouse gases.

This study advances scientific understanding of the magnitude of carbon sequestration that could be achieved through conservation (securing existing carbon stocks) and restoration (creating new carbon stocks) of freshwater mineral soil wetlands on agricultural landscapes. Within an agricultural landscape in southern Ontario (Canada), 65,261 wetlands comprising 63,135 ha were lost. Of these, 6,899 wetlands comprising 5,198 ha were “easy-to-restore” wetlands, defined as wetlands that were small (&lt;0.5 ha), with no hydrological inflow or outflow, and that were drained by a drainage ditch and could be restored by plugging the drainage ditch. Within these easy-to-restore wetlands, a chronosequence of wetlands that covered a range of restoration ages [i.e., drained (0 years), 15 years, 25 years, 40 years, and intact marshes] was established to capture potential changes in rates of sedimentation and organic carbon (OC) sequestration with restoration age. Three sediment cores were collected at the center of the open-water portion of the wetland and segmented in the field. In the lab, each individual segment from each core was dried, sieved through a 2-mm mesh, weighed and analyzed for 137Cs and 210Pb radioisotopes and OC. OC stocks (35.60 Mg ha–1) and OC sequestration rates (0.89 Mg C ha–2 yr–1) in wetlands restored for 40 years were comparable to if not marginally larger than intact wetlands, suggesting that restoration promotes OC sequestration but that an initial recovery phase of up to 25 years or more is needed before returning to a pre-drainage equilibrium. An economic analysis to compare the costs and benefits of wetland conservation and restoration was then conducted. The benefit-cost analysis revealed that the financial benefits of carbon sequestration are greater than the financial costs over a 30-year time horizon for retaining wetlands but not for restoring wetlands. The breakeven costs such that wetland restoration is economically feasible based on current carbon price projections is estimated to be $17,173 CAD ha–1 over the 30-year time horizon; any wetland restoration project that costs this amount or less could be justified on economic grounds based solely on the carbon benefits. This study’s findings indicate that wetlands are important nature-based climate solutions, but that incentivizing their use through a carbon market will require either scientific innovations to reduce restoration costs or increase carbon sequestration rates, or stacking carbon benefits with other ecosystem service benefits into a comprehensive market for nature-based climate solutions.

Riparian buffer strip guidelines are under scrutiny in the River Njoro Watershed in Kenya. This study investigated soil properties (bulk density, carbon, nitrogen, and phosphorus) in different land use types (small scale agriculture in recent settlements, mixed agriculture in established peri-urban settlements, largescale commercial agriculture, and the gazetted forest reference condition) and their adjacent buffer strips. Bulk density, carbon, nitrogen, and phosphorus within 30-m riparian buffer strips adjacent to recent settlement land use areas were similar to those of the gazetted forest reference condition, but only bulk density of the buffer strips adjacent to peri-urban and commercial agriculture land use areas were similar to the gazetted forest reference condition. Phosphorus is a sensitive indicator of the impacts of human activity, as increased concentrations were observed with increasing scale of land use activity. For riparian buffers adjacent to recent settlements, soil phosphorus was significantly higher in buffers narrower than 30 m (5.01 mg P kg −1 ) than gazetted forest (3.40 mg P kg −1 ) but not significantly different for riparian buffers wider than 30 m (3.81 mg P kg −1 ) compared to gazetted forest. Based on the research, it is recommended that policies governing riparian buffer strips become (1) stricter, with the current "maximum" of 30 m considered a minimum; and (2) adaptive, with 30 m used in smallscale agricultural areas, and wider riparian buffer strips used in medium-and large-scale agricultural areas.

Much of Canada’s industrial sector is driven by natural resources and relies heavily on provisioning services supplied by the boreal zone. However, the sometimes intensive processes used by resource-based industries and their associated infrastructure have significantly altered the region, creating concerns over the future socio-ecological health of the boreal zone. Addressing these concerns will require industries reliant on natural resources from the boreal zone to innovate their processes, management, and infrastructure to improve extraction efficiency while contributing to society’s increasing expectations related to sustainability. Here, we explore past, current, and future trends in industrial innovation and infrastructure in the boreal zone for forestry, mining, pulp and paper, oil and gas, and renewable sources of power generation. We assess the role of innovation on the future socio-ecological state of the boreal zone by considering interactions between innovation in industry and infrastructure and other key drivers of change in the boreal, such as atmospheric changes, changing demands for nonprovisioning and provisioning ecosystem services, governance, and demographics and social values. We present future scenarios highlighting three divergent trajectories of change in boreal ecosystems based on past and current states of innovation in industry and infrastructure. We suggest that minimizing impacts of natural resource extraction activities in the boreal zone will only be possible through innovation directly focused on reducing the human footprint on the landscape. Innovation in the information technology sector related to process, management, and end products within these industries and placing greater emphasis on cross-sectoral collaboration will be key to achieving this goal.

The magnitude of net soil nitrous oxide (N2O) production from a snow‐covered catchment in a northern temperate forest was investigated. There was considerable net soil N2O‐N production and consumption through the snowpack, ranging from −6.6 to 26.2 g‐N ha−1 d−1. There was no difference in net N2O production among topographic positions despite significant variation in soil moisture, reduction‐oxidation conditions, and pore water dissolved organic carbon and nitrate. Soil temperatures did not vary among topographic positions, suggesting that temperatures at or above the freezing point allow N2O production to proceed under the snowpack. Redox conditions were lower at wetland positions compared to lowlands and uplands, suggesting that the biogeochemical pathway of N2O production varies with topography. Over the entire nongrowing season, 1.5 kg of N2O‐N was exported to the atmosphere from the 6.33 ha catchment, representing 31% of the growing season N2O‐N production. These results suggest that winter is an active time for gaseous N production in these forests and that N2O production under the snowpack represents an often unmonitored flux of N from catchments.