We determined the concentrations of lead and cadmium in edible parts of Colocasiaesculenta, Amaranthusspp. and Ipomoea batata cultivated on farms in industrially polluted sections of Nyabugogo marsh (Kigali, Rwanda) and quantified metal intake by consumers of these crops. We report that metal concentrations in crops were within EU limits. The highest metal concentrations were found in Amaranthusspp. leaves (lead = 0.31 mg/kg and cadmium = 0.03 mg/kg) and the lowestin I. batata (lead = 0.02 mg/kg and cadmium = 0.01 mg/kg). Conversely, metal intake through these crops by adults in a surveyed community exceeded thresholds prescribed by the World Health Organization (WHO). Based on crop consumption quantities, dietary lead intake by adults exceeded the recommended maximum by as much as seven and four orders of magnitude through Amaranthusspp and C. esculenta,respectively. Cadmium intake exceeded the WHO recommended maximum by two (Amaranthusspp and C. esculenta)and three (I. batata) orders of magnitude.

Acacia mearnsii is an introduced Australian acacia in South Africa and has invaded more than 2.5 million ha, primarily establishing in rangeland and riparian areas. Because acacias have the capability to fix N, A. mearnsii invasions may fundamentally change N dynamics in invaded systems. This study compares biological N2-fixation in the alien invasive A. mearnsii and the native A. caffra growing in a grassland riparian zone in the Komati Gorge Reserve, Mpumalanga, South Africa. A 15N natural abundance field survey suggested that both mature alien and native acacias fix N under current conditions in the riparian zone. Significantly depleted δ15N was observed in both acacias relative to reference species, although variation in δ15N was not correlated with N concentrations. Calculated contributions of N2-fixation (%Ndfa) suggest that alien acacias fix significantly more of their N than native acacias (~75 ± 5% SE and 53 ± 9% SE, respectively). There was a larger variation in δ15N and %Ndfa in the native acacia, suggesting relatively high plasticity in its N2-fixation contributions. This plasticity was interpreted as a facultative N2-fixation strategy for the native acacia, while the N2-fixation strategy of the alien acacia remained unclear. Our results emphasize the importance of potentially elevated N inputs through N2-fixation by invasive legumes in invaded landscapes. Furthermore, they suggest that N2-fixation by invasive acacias may not respond to fine-scale patchiness in soil N in the same manner as native acacias, making them potential contributors to N excess in Southern Africa.

Quantification of a relationship between salmon escapement in rivers and riparian tree-ring δ15N could allow reconstruction of prehistorical salmon abundance. Unfortunately, attempts to quantify this link have met with little success. We examined the feasibility of the approach using natural abundance of δ15N in riparian tree rings formed before and after extirpation of salmon and 15N tracer studies in a river and riparian soils. We concluded that (i) extractable (sap) N must be removed for interpretation of tree-ring δ15N because it contains up to 78% of the N in wood, is mobile, and differs from structural N in isotopic composition, (ii) no significant change in structural tree-ring δ15N was associated with salmon extirpation in a natural system, (iii) 500‰ 15NH4+ added to a stream was detected in riparian tree rings spanning at least 8 years, demonstrating interring movement of N that confounds detection of an annual signal, and (iv) addition of 28 000‰ 15NH4+ to riparian soils at a rate equaling 7.25 kg salmon·50 m–2 resulted in maximum tree-ring δ15N of ∼100‰–600‰. Thus, the calculated maximum signal possible from salmon was 0.08‰–0.43‰, which is within the range of natural variation. Evidence suggested that neither total nor structural tree-ring δ15N was useful for reconstructing salmon abundance.

Summary 1. This study examined the seemingly paradoxical proliferation of invasive, N2‐fixing broom (Cytisus scoparius) and gorse (Ulex europaeus) in N‐saturated riparian areas of intensive agricultural land in Canterbury, New Zealand. 2. A field study of natural abundance δ15N suggested that broom and gorse along the Selwyn River fix approximately three times more N than they take up from soils, and are thus a potentially large source of N in the landscape. Broom N fixation rates based on mass balance calculations from a glasshouse study were similar. 3. In the controlled glasshouse study, broom grown at both c. 1× and 6.5× field NO3− supply fixed N at the same rate per unit biomass (0.061 mg N day−1 g−1 dry wt) over a 9‐month period. Broom plants grown under the high‐N supply, however, grew c. 1.6 times larger, and thus fixed more N per plant. Above‐to‐below‐ground biomass ratios and %N in above‐ and below‐ground pools were the same under the two levels of N supply. 4. Each broom plant in the greenhouse study contributed at least 0.02 g N year−1 to soils, but leaching from the soils was surprisingly low (<2% of total plant and soil stocks) suggesting that plants less than 1 year old are not contributing substantially to high NO3− concentrations in Selwyn ground and surface water. 5. Synthesis. This study shows that both broom and gorse growing in the Selwyn riparian area are an additional source of bioactive N in this N‐saturated ecosystem. Additionally, broom grows more quickly as N availability increases and therefore fixes more N per plant. This suggests a positive feedback whereby agricultural nutrient pollution leads to increased per‐plant N2 fixation in broom, and probably in gorse, given the taxonomic and physiological similarity of the species. The Selwyn is representative of a large number of New Zealand rivers with riparian zones that are dominated by invasive N2 fixers. The likelihood that these invasive plants increase the amount of bioactive N in rivers and downstream ecosystems presents new considerations and challenges for management.

We present the results of an effort to develop a national-scale predictive model to describe the current condition of shallow, coastal New Zealand lakes. Comprehensive biological, physical and chemical data from 45 shallow, coastal lakes are compared to catchment-level disturbance indices (indigenous vegetation loss, nutrient loading, invasive species) derived by New Zealand’s Waters of National Importance (WoNI) Programme. Few strong relationships were identified, but some general patterns were evident: lakes in disturbed catchments tended to have a higher trophic state, higher pH, reduced light penetration, lower submerged macrophyte cover, smaller food webs, lower rotifer diversity, and a larger proportion of introduced fish species. We discuss these patterns in the context of “ecological integrity” (EI), a subjective descriptor used in WoNI and other management programmes. A lack of historical data and difficulties in quantifying “integrity” remain persistent challenges for linking science with management for EI. Relationships between the WoNI indices and measured limnological conditions were not strong enough to build a predictive, nationally relevant model for estimating the EI. However, we present an alternative method for estimating EI based on expert assessment; expert assessment EI was significantly correlated to both WoNI pressure indices and many of the limnological variables measured here.

Here we review developments in paleoecological reconstruction of Pacific salmon abundance and discuss the new management context and implications provided by the reconstructions. Currently, two approaches are yielding long term reconstructions of salmon abundance over the last hundreds to thousands of years. First, in sockeye salmon Oncorhynchus nerka nursery lakes, the abundance of adult salmon is reflected in chemical and biological characteristics of lake sediments. These indicators have been used to reconstruct patterns of salmon abundance over 2,500 years and are compared at several points by archeological data. Second, emerging techniques using riparian tree-ring-growth have produced sub-decadal resolution reconstructions of stream-spawning sockeye, Chinook O. tshawytscha, pink O. gorbuscha, and chum O. keta salmon populations over the last 150-350 years. Paleoecological reconstructions provide important insights into salmon abundance and their variability prior to European settlement of western North America. For example, sediment-based reconstructions show periods of naturally low sockeye salmon abundance at similar to A.D. 1800 and from similar to A.D. 0-700 in Alaskan lakes, and tree-ring based reconstructions show river-specific patterns in abundance with cycles of 21-68 years in duration. Both types of reconstruction also suggest relatively rapid, natural "recovery" of salmon populations after periods of low abundance. As additional reconstructions become available and a more synthetic understanding of them is developed, paleoecological reconstructions will allow better evaluation of management paradigms (e.g., the long-term fidelity of Pacific Decadal Oscillation cycles and regional salmon abundance) as well as identification of additional patterns that cannot be extracted from limited historical data sets. Paleoecological perspectives play a potentially important role in changing societal expectations of salmon resources by recognizing natural variations in abundance. Such expectations, if tempered by acknowledging natural changes in salmon productivity, can be incorporated into flexible models, management and restoration strategies.

We compared processing and fate of dissolved NO3- in two New England salt marsh ecosystems, one receiving natural flood tide concentrations of approximately 1-4 micromol NO3-/ L and the other receiving experimentally fertilized flood tides containing approximately 70-100 micromol NO3-/ L. We conducted simultaneous 15NO3- (isotope) tracer additions from 23 to 28 July 2005 in the reference (8.4 ha) and fertilized (12.4 ha) systems to compare N dynamics and fate. Two full tidal cycles were intensively studied during the paired tracer additions. Resulting mass balances showed that essentially 100% (0.48-0.61 mol NO3-N.ha(-1).h(-1)) of incoming NO3- was assimilated, dissimilated, sorbed, or sedimented (processed) within a few hours in the reference system when NO3- concentrations were 1.3-1.8 micromol/L. In contrast, only 50-60% of incoming NO3- was processed in the fertilized system when NO3- concentrations were 84-96 micromol/L; the remainder was exported in ebb tidewater. Gross NO3- processing was approximately 40 times higher in the fertilized system at 19.34-24.67 mol NO3-N.ha(-1).h(-1). Dissimilatory nitrate reduction to ammonium was evident in both systems during the first 48 h of the tracer additions but <1% of incoming 15NO3- was exported as 15NH4+. Nitrification rates calculated by 15NO3- dilution were 6.05 and 4.46 mol.ha(-1).h(-1) in the fertilized system but could not be accurately calculated in the reference system due to rapid (<4 h) NO3- turnover. Over the five-day paired tracer addition, sediments sequestered a small fraction of incoming NO3-, although the efficiency of sequestration was 3.8% in the reference system and 0.7% in the fertilized system. Gross sediment N sequestration rates were similar at 13.5 and 12.6 mol.ha(-1).d(-1), respectively. Macrophyte NO3- uptake efficiency, based on tracer incorporation in aboveground tissues, was considerably higher in the reference system (16.8%) than the fertilized system (2.6%), although bulk uptake of NO3- by plants was lower in the reference system (1.75 mol NO3-.ha(-1).d(-1)) than the fertilized system (approximately 10 mol NO3-.ha(-1).d(-1)). Nitrogen processing efficiency decreased with NO3- load in all pools, suggesting that the nutrient processing capacity of the marsh ecosystem was exceeded in the fertilized marsh.

We examined the effects of increased nutrient availability on nitrogen (N) dynamics in dominant New England salt marsh plants (tall and stunted Spartina alterniflora and S. patens) using paired large-scale nutrient and (NO3-)-N-15 tracer additions. This study is one component of a long-term, large-scale, salt marsh nutrient and trophic manipulation study (the Trophic Cascades and Interacting Control Processes in a Detritus-based Aquatic Ecosystem [TIDE] Project). We compared physiological variables of plants in fertilized (similar to 17x ambient N and P in incoming tidal water) and reference marsh systems to quantify NO3- uptake and uptake efficiency, allocation of N to tissues, end-of-season N resorption, leaf litter quality and other potential responses to increased nutrient availability. Reference system plants sequestered similar to 24.5 g NO3-N ha(-1) d(-1) in aboveground pools during midsummer, while fertilized plants sequestered similar to 140 g NO3-N ha(-1) d(-1). However, NO3- uptake efficiency (% of total incoming NO3-N sequestered aboveground) was higher in the reference system (16.8%) than in the fertilized system (2.6%), suggesting that our fertilization rate (similar to 70 mu M NO3- in incoming water) approaches or exceeds the uptake saturation point for this vegetation community. Leaf litter quality was clearly affected by N availability; N resorption efficiency was lower in all plants of the fertilized system; senesced leaves from the fertilized creek contained similar to 43% (tall S. alterniflora), 23 % (stunted S. alterniflora) and 15% (S. patens) more N per unit biomass than reference creek leaves.

We use relationships between modern Pacific salmon (Oncorhynchus spp.) escapement (migrating adults counted at weirs or dams) and riparian tree-ring growth to reconstruct the abundance of stream-spawning salmon over 150-350 years. After examining nine sites, we produced reconstructions for five mid-order rivers and four salmon species over a large geographic range in the Pacific Northwest: chinook (O. tschwatcha) in the Umpqua River, Oregon, USA; sockeye (O. nerka) in Drinkwater Creek, British Columbia, Canada; pink (O. gorbuscha) in Sashin Creek, southeastern Alaska, USA; chum (O. keta) in Disappearance Creek, southeastern Alaska, USA; and pink and chum in the Kadashan River, southeastern Alaska, USA. We first derived stand-level, non-climatic growth chronologies from riparian trees using standard dendroecology methods and differencing. When the chronologies were compared to 18-55 years of adult salmon escapement we detected positive, significant correlations at five of the nine sites. Regression models relating escapement to tree-ring growth at the five sites were applied to the differenced chronologies to reconstruct salmon abundance. Each reconstruction contains unique patterns characteristic of the site and salmon species. Reconstructions were validated by comparison to local histories (e.g., construction of dams and salmon canneries) and regional fisheries data such as salmon landings and aerial surveys and the Pacific Decadal Oscillation climate index. The reconstructions capture lower-frequency cycles better than extremes and are most useful for determination and comparison of relative abundance, cycles, and the effects of interventions. Reconstructions show lower population cycle maxima in both Umpqua River chinook and Sashin Creek pink salmon in recent decades. The Drinkwater Creek reconstruction suggests that sockeye abundance since the mid-1990s has been 15-25% higher than at any time since 1850, while no long-term deviations from natural cycles are detected for salmon in the Kadashan River or in Disappearance Creek. Decadal-scale cycles in salmon abundance with periods of 25-68 years were detected in all of the reconstructions. This novel approach provides river-specific, long-term perspectives on salmon abundance and cycles. Additionally, it provides a new frame of reference for maintaining and rebuilding individual stocks and for striking a balance between societal demands and the limited, always-changing salmon resource.

Riparian systems epitomize heterogeneity. As transitional semiterrestrial areas influenced by water, they usually extend from the edges of water bodies to the edges of upland terraces. Riparian systems often exhibit strong biophysical gradients, which control energy and elemental fluxes, and are highly variable in time and space. These attributes contribute to substantial biodiversity, elevated biomass and productivity, and an array of habitats and refugia. Focusing on riparian systems of medium-sized floodplain rivers, we describe heterogeneity at multiple space and time scales, illustrate interactions among scales, and propose a conceptual model integrating major system components. We show how climatic and geologic processes shape an array of physical templates, describe how disturbances redistribute materials, and illustrate how soils and subsurface processes form and are sustained. Collectively, these processes strongly influence plant productivity and fluxes of channel-shaping large woody debris (LWD). Ultimately, riparian ecosystem function integrates climate (past and present), geologic materials and processes, soil development and attendant microbial transformations, subsurface characteristics, plant productivity, animal activities, and LWD-and the active, continuous and variable feedbacks between the individual components.

Decision-makers concerned with salmon or their stream habitats are faced with many persistent, difficult questions including: how large and variable were these populations before European settlement? Here, we examine the feasibility of reconstructing salmon abundance using links between marine nutrients carried upstream by Pacific salmon (Oncorhynchus spp.) and growth of dominant riparian trees in two Alaskan systems. We employ standard dendrochronology methods and regression models to quantify relationships between annual tree-ring growth, salmon escapement, and the climate pattern that affects oceanic production of Northeast Pacific salmon stocks, the Pacific Decadal Oscillation (PDO). We find that known, annual salmon escapement is significantly related to tree-ring growth at two sites in the Pacific coastal rainforest (PCRF) (r2 = 0.23, P < 0.05 at each site), but not at two sites in the boreal forest. We then use relationships established at PCRF sites to reconstruct preliminary salmon spawning abundances to 1820 A.D. The PDO was not correlated with local 19-yr salmon escapement records and could not be used in reconstructions. Reconstructions compare favorably to southeastern Alaska fisheries catch data from 1924 to 1994 (Pearson correlation = 0.301 [P = 0.02] and 0.401 [P < 0.01]). This study demonstrates the promise and utility of dendrochronology for reconstructing salmon returns to streams.

Detrimental effects of introduced fishes on native amphibian populations have prompted removal of introduced cutthroat (Oncorhynchus clarki), rainbow (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis) from naturally fishless lakes at Mt. Rainier National Park Washington (U.S.A.). Using paleolimnological indicators (diatoms, invertebrates, and sediment characteristics) in eight 480-year-old sediment cores from eight lakes we (1) derived estimates of baseline environmental conditions and natural variation, (2) assessed the effects of stocking naturally fishless lakes and (3) determined whether lakes returned to predisturbance conditions after fish removal (restoration). Diatom floras were relatively stable between 315 and 90 years before present in an lakes; we used this time period to define lake;specific "baseline" conditions. Dissimilarity analyses of diatoms revealed sustained, dramatic changes in diatom floras that occurred approximately, 80 years ago (when fish were introduced) in four of five stocked lakes whereas the diatom floras in two unstocked lakes had nor changed significantly in the last 315 years Diatoms were not preserved in an eighth lake. State changes also occurred in two lakes over 200 years before European settlement of the Pacific Northwest Preserved invertebrate densities fluctuated dramatically over time in all cores, providing a Pool reference for assessing the effects of fishes. Nevertheless, fish-invertebrate interactions have been demonstrated in other paleolimnological studies and may be useful for lower-elevation or more productive lakes Because diatom communities have not returned to predisturbance assemblages in restored lakes even 20-30 years after fish removal, we conclude that Mt Rainier lakes were not successfully restored by the removal of fishes.