Jana E. Compton

Nitrogen Export from Forested Watersheds in the Oregon Coast Range: The Role of N2-fixing Red Alder

AbstractVariations in plant community composition across the landscape can influence nutrient retention and loss at the watershed scale. A striking example of plant species importance is the influence of N2-fixing red alder (Alnus rubra) on nutrient cycling in the forests of the Pacific Northwest. To understand the influence of red alder on watershed nutrient export, we studied the chemistry of 26 small watershed streams within the Salmon River basin of the Oregon Coast Range. Nitrate and dissolved organic nitrogen (DON) concentrations were positively related to broadleaf cover (dominated by red alder: 94% of basal area), particularly when near-coastal sites were excluded (r 2 = 0.65 and 0.68 for nitrate-N and DON, respectively). Nitrate and DON concentrations were more strongly related to broadleaf cover within entire watersheds than broadleaf cover within the riparian area alone, which indicates that leaching from upland alder stands plays an important role in watershed nitrogen (N) export. Nitrate dominated over DON in hydrologic export (92% of total dissolved N), and nitrate and DON concentrations were strongly correlated. Annual N export was highly variable among watersheds (2.4–30.8 kg N ha−1 y−1), described by a multiple linear regression combining broadleaf and mixed broadleaf–conifer cover (r2 = 0.74). Base cation concentrations were positively related to nitrate concentrations, which suggests that nitrate leaching increases cation losses. Our findings provide evidence for strong control of ecosystem function by a single plant species, where leaching from N saturated red alder stands is a major control on N export from these coastal watersheds.

Ecosystem services altered by human changes in the nitrogen cycle: a new perspective for US decision making

Human alteration of the nitrogen (N) cycle has produced benefits for health and well-being, but excess N has altered many ecosystems and degraded air and water quality. US regulations mandate protection of the environment in terms that directly connect to ecosystem services. Here, we review the science quantifying effects of N on key ecosystem services, and compare the costs of N-related impacts or mitigation using the metric of cost per unit of N. Damage costs to the provision of clean air, reflected by impaired human respiratory health, are well characterized and fairly high (e.g. costs of ozone and particulate damages of

Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies

28 per kg NO(x)-N). Damage to services associated with productivity, biodiversity, recreation and clean water are less certain and although generally lower, these costs are quite variable (<

Juvenile Coho Salmon Growth and Survival across Stream Network Seasonal Habitats

2.2-56 per kg N). In the current Chesapeake Bay restoration effort, for example, the collection of available damage costs clearly exceeds the projected abatement costs to reduce N loads to the Bay (

Mangrove-Exported Nutrient Incorporation by Sessile Coral Reef Invertebrates

8-15 per kg N). Explicit consideration and accounting of effects on multiple ecosystem services provides decision-makers an integrated view of N sources, damages and abatement costs to address the significant challenges associated with reducing N pollution.

Coho salmon dependence on intermittent streams

Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (< 1 week after 15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3-18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C:N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N x ha(-1) x yr(-1) above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.

NITROGEN RETENTION ACROSS A GRADIENT OF 15N ADDITIONS TO AN UNPOLLUTED TEMPERATE FOREST SOIL IN CHILE

Abstract Understanding watershed-scale variation in juvenile salmonid survival and growth can provide insights into factors influencing demographics and can help target restoration and mitigation efforts for imperiled fish populations. We assessed growth, movement, and apparent overwinter survival of individually tagged juvenile coho salmon Oncorhynchus kisutch in a coastal Oregon watershed from June 2002 to June 2003 and related growth and survival parameters to stream characteristics. Fall body size of juvenile coho salmon was a good predictor of smolt size and survival, but smolt size was also influenced by overwintering location. This was due to strong spatial patterns in winter growth rates associated with residency and movement into a small intermittent tributary. Though nearly dry in midsummer, this stream supported high densities of spawning coho salmon in the fall, and juveniles rearing there exhibited relatively high growth rates and emigrated as larger smolts. Improved winter growth and surviva...

Ecological and water quality consequences of nutrient addition for salmon restoration in the Pacific Northwest

Coastal mangrove forests were historically considered as a source of organic matter (OM) for adjacent marine systems due to high net primary production; yet recent research suggesting little uptake through the food web because of low nutritional quality, challenges the concept of trophic linkage between mangrove forests and coral reefs. To examine the importance of mangrove forests to coral reef nutrient availability, we examined sessile reef-forming invertebrate consumers including hard corals, sponges, a bivalve mollusc, polychaete annelid and tunicate, and potential sources of OM (decaying mangrove leaves, microalgae, macroalgae, and seagrass) in Bocas del Toro, Panama. Using stable isotope analyses of δ34S and δ13C and a concentration-dependent version of the IsoSource mixing model, we were able to discriminate among and determine the range of potential contributions of our four OM sources to consumers. Contributions of microalgae and macroalgae were often indeterminate due to high variability, yet seagrass and mangrove contributions were often substantial. Mangrove OM ranged across sites and species of filter feeders from 0 to 57%, 7 to 41%, and 18 to 52% for sponges, file clams, and feather duster worms, respectively. Mangrove contribution to corals (Acropora cervicornis, Agaricia fragilis, Agaricia tenuifolia, Montastrea annularis, Diploria sp.) ranged from 0 to 44%. To examine whether OM contribution varied with distance from mangroves, we conducted a sponge transplant experiment that demonstrated declining mangrove contribution across three sponge species with increasing distance from the shore. These results supported the hypothesis of mangrove-coral reef nutrient linkages, providing the first evidence that mangrove inputs of OM to sessile invertebrates are substantial, accounting for 0–57% of the composition.

Reactive nitrogen inputs to US lands and waterways: how certain are we about sources and fluxes?

In February 2006, the US Supreme Court heard cases that may affect whether intermittent streams are jurisdictional waters under the Clean Water Act. In June 2006, however, the cases were remanded to the circuit court, leaving the status of intermittent streams uncertain once again. The presence of commercial species, such as coho salmon (Oncorhynchus kisutch), can be an important consideration when determining jurisdiction. These salmon spawn in the upper portions of Oregon coastal stream networks, where intermittent streams are common. In our study of a coastal Oregon watershed, we found that intermittent streams were an important source of coho salmon smolts. Residual pools in intermittent streams provided a means by which juvenile coho could survive during dry periods; smolts that overwintered in intermittent streams were larger than those from perennial streams. Movement of juvenile coho into intermittent tributaries from the mainstem was another way in which the fish exploited the habitat and illustrates the importance of maintaining accessibility for entire stream networks. Loss of intermittent stream habitat would have a negative effect on coho salmon populations in coastal drainages, including downstream navigable waters.

Cost of reactive nitrogen release from human activities to the environment in the United States

Accelerated nitrogen (N) inputs can drive nonlinear changes in N cycling, retention, and loss in forest ecosystems. Nitrogen processing in soils is critical to understanding these changes, since soils typically are the largest N sink in forests. To elucidate soil mechanisms that underlie shifts in N cycling across a wide gradient of N supply, we added 15NH415NO3 at nine treatment levels ranging in geometric sequence from 0.2 kg to 640 kg N·ha−1·yr−1 to an unpolluted old-growth temperate forest in southern Chile. We recovered roughly half of 15N tracers in 0–25 cm of soil, primarily in the surface 10 cm. Low to moderate rates of N supply failed to stimulate N leaching, which suggests that most unrecovered 15N was transferred from soils to unmeasured sinks above ground. However, soil solution losses of nitrate increased sharply at inputs >160 kg N·ha−1·yr−1, corresponding to a threshold of elevated soil N availability and declining 15N retention in soil. Soil organic matter (<5.6 mm) dominated tracer retention at low rates of N input, but coarse roots and particulate organic matter became increasingly important at higher N supply. Coarse roots and particulate organic matter together accounted for 38% of recovered 15N in soils at the highest N inputs and may explain a substantial fraction of the “missing N” often reported in studies of fates of N inputs to forests. Contrary to expectations, N additions did not stimulate gross N cycling, potential nitrification, or ammonium oxidizer populations. Our results indicate that the nonlinearity in N retention and loss resulted directly from excessive N supply relative to sinks, independent of plant–soil–microbial feedbacks. However, N additions did induce a sharp decrease in microbial biomass C:N that is predicted by N saturation theory, and which could increase long-term N storage in soil organic matter by lowering the critical C:N ratio for net N mineralization. All measured sinks accumulated 15N tracers across the full gradient of N supply, suggesting that short-term nonlinearity in N retention resulted from saturation of uptake kinetics, not uptake capacity, in plant, soil, and microbial pools.