M. Robbins Church

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.

Sulfur retention at intensively studied sites in the U.S. and Canada

We compiled and summarized current literature on S input/output budgets for intensively studied sites and soil plots in the U.S. and Canada and found S retention to be related to both soil order and extent of the last glaciation (Wisconsinan). Zero net retention is associated with Spodosols and was found only at sites north of the limit of Wisconsinan glaciation. Sites south of the limit of glaciation appear to be retaining from 20 to 90% of incoming S. These findings support the hypothesis that there exist regional variations in S retention in North America. Such variations are important in determining and predicting effects of acidic deposition on surface water chemistry.

Juvenile Coho Salmon Growth and Survival across Stream Network Seasonal Habitats

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

Salmon runs have declined over the past two centuries in the Pacific Northwest region of North America. Reduced inputs of salmon-derived organic matter and nutrients (SDN) may limit freshwater production and thus establish a negative feedback loop affecting future generations of fish. Restoration efforts use the rationale of declining SDN to justify artificial nutrient additions, with the goal of reversing salmon decline. The forms of nutrient addition include introducing salmon carcasses, carcass analogs (processed fish cakes), or inorganic fertilizers. While evidence suggests that fish and wildlife may benefit from increases in food availability as a result of carcass additions, stream ecosystems vary in their ability to use nutrients to benefit salmon. Moreover, the practice may introduce excess nutrients, disease, and toxic substances to streams that may already exceed proposed water quality standards. Restoration efforts involving nutrient addition must balance the potential benefits of increased foo...

Regional patterns of sulfur retention in watersheds of the Eastern US

Retention of S was estimated in watersheds of the Eastern US by calculating S input-output budgets for 678 lake and reservoir watershed systems in the Northeast (NE), 98 lake and reservoir and 61 stream systems of the Southern Blue Ridge Province (SBRP) and 56 stream systems of Shenandoah National Park (SNP). Budgets were determined based on estimates of deposition and output (as surface water) for each of the sites. A variety of estimates of total S deposition were used. Percent S retention is high for sites in the SBRP and SNP but is distributed around zero for sites in the NE. These findings lend support to the hypothesis that patterns exist in S retention relative to the extent of the Late Wisconsinan glaciation.

Maps of regional evapotranspiration and runoff/precipitation ratios in the northeast United States

Regional maps of evapotranspiration (ET) and runoff/precipitation ratios (RP) are rare for the United States. We have found mapping of ET and RP to be a useful part of our work on runoff mapping, which in turn was a necessary part of our assessments of effects of acidic deposition. Maps of ET and RP could be useful in other water resource analyses as well. Toward this end we present maps of these variables that we have prepared for the northeastern United States. We compute ET and RP from the water balance equation with measured runoff and precipitation and (in one case) modeled estimates of precipitation. We have mapped ET and RP in three different ways. First, we have mapped them by Major Land-Use Resource Areas (MLRA). We have performed this mapping for both a long-term period (1951–1980) and an especially wet water year, water-year 1984 (WY84). Second, we have mapped ET and RP using an automated contouring procedure in association with modeled estimates of precipitation from PRISM (Precipitation-elevation Regressions on Independent Slopes Model). Third, we have manually contoured the variables based on measured values of runoff and precipitation as they appear to relate to elevation, land use, and vegetation. Our maps compare well with each other and with the relatively few prior efforts at such mapping for the region. Our findings indicate that ET tends to be much more conservative over time than RP, which tended to be greater in the wet year (WY84). As would be expected, the three approaches have relative strengths and weaknesses. Mapping by MLRA may be more useful when measured estimates are few or when lack of local expertise limits contouring subjectively. Contouring allows for more detailed representation of patterns. Automated contouring has the advantages of efficiency and reproducibility, whereas manual contouring allows the exercise of potentially more accurate expert local knowledge, when it exists.

Regional relationships between geomorphic/hydrologic parameters and surface water chemistry relative to acidic deposition

Abstract We determined geomorphic and hydrologic parameters for 144 forested, lake watersheds in the Northeast (NE) of the United States based primarily on measurements from topographic maps. These parameters were used to test for relationships with selected surface water chemistry relevant to acidic deposition. Analyses were conducted on regional and subregional scales delineated based on soils, land use, physiography, total sulfur deposition and statistical clustering of selected geomorphic/hydrologic parameters. Significant relationships were found among the geomorphic/hydrologic parameters and the surface water chemistry for the NE. Elevation had the most significant relationship with surface water chemistry, particularly in the mountainous areas of the NE. Other factors occurring consistently as significant predictors of surface water chemistry were maximum relief, relief ratio, runoff, and estimates of basin elongation. Results suggest that elevational parameters might be surrogates for other watershed characteristics, such as soils or spatial deposition patterns. Stream order was a significant class variable with lower order systems tending to be associated with low pH and acid neutralizing capacity high sulfate and total aluminum. Analysis at the sub-regional level improved the correlations among the descriptive parameters and surface water chemistry over the findings for the total NE. This improvement in correlation is probably due to reduced heterogeneity within the data at the sub-regional level. Also, stratifying the data based on factors such as soils and sulfur deposition removes some of the influence these factors have on surface water chemistry.

Hierarchical Modeling of Late-Summer Weight and Summer Abundance of Juvenile Coho Salmon across a Stream Network

Abstract Spatial variation in stream habitat quality can lead to network-level patterns in the survival and growth of juvenile coho salmon Oncorhynchus kisutch that provide important insights into the factors influencing the freshwater population dynamics of this species. Our objectives were to quantify the relationships among summer habitat conditions, coho salmon density, and coho salmon parr abundance and weight across an extensive stream network over 3 years. We used hierarchical linear models to assess the factors influencing coho salmon weight and abundance at the levels of individual fish (fork length and parasite burden), habitat unit (surface area, cover, and density), reach (temperature and density) and stream (total nitrogen, soluble reactive phosphorus, and discharge). Habitat-unit-level surface area and stream-level minimum discharge were important predictors of both the abundance and weight of coho salmon parr. An area × discharge interaction term was also important in models of weight and r...

Direct/delayed response project: Predicting future long‐term effects of acidic deposition on surface water chemistry

In 1984 the U.S. Environmental Protection Agency, as part of the National Acid Precipitation Assessment Program, initiated a project to estimate potential future effects of acidic deposition on the chemistry of lakes and streams. This project, the Direct/Delayed Response Project (DDRP), has focused its attention on surface waters in regions of the eastern U.S. thought to be most vulnerable to effects of acidic deposition. The project hascombined regional surface water chemistrydata gathered by EPAs National Surface Water Survey with a unique regional watershed and soil survey under take n within the DDRP.The project is applying a variety of analyses, including the use of three independently derived watershed models of acidic deposition effects. This article describes the design of the DDRP and presents some of its preliminary products.

Automated approaches for regional runoff mapping in the northeastern United States

Abstract Recently, we have used automated procedures to develop simple, yet accurate, ways to create runoff contour maps. Our goal was to produce maps as accurate as those now produced by manual methods. We developed eight procedures based on simple water balance methods and regression techniques to produce a map for our test case, Water-Year 1984 for the northeastern United States. Our maps are produced by linear interpolation of (1) gaged runoff at watershed centroids, and (2) runoff estimated at a set of geographic locations (precipitation stations) via each of the eight procedures. We evaluated the maps both qualitatively and quantitatively. We visually compared the automated procedure maps with a manual map produced by the U.S. Geological Survey. In general, visual agreement was very good. We then statistically compared the estimated runoff at the precipitation stations with values interpolated from the manual map. Comparing simple mean runoff, we found that two of the automated procedures gave the best results when compared with the manual map (MAN84; mean annual runoff = 84.0 cm). One method used gauged runoff values only (GAGE84; mean annual runoff = 83.3 cm) and the other used Water-Year 1984 mean regional runoff-to-precipitation ratios (MN84RP; meanannualrunoff = 82.9 cm). Because of the over-generalized appearance of the GAGE84 map compared with the manual map, we preferred the MN84RP method. Next, we performed an uncertainty analysis for five of our eight procedures. In this analysis, we withheld gauged data in the production of the maps and then compared these data with interpolated values from the maps that were produced. The MN84RP procedure and a procedure using a regression approach (REG__R) had the lowest mean interpolation error. We determined that these two procedures, MN84RP and REG__R, produce the most accurate maps on a regional basis and compare favorably with the manual map (i.e. mean interpolation errors of − 1.8% and −0.7% vs. the manual method mean error of 0.9%). The results of our work indicate that simple automated procedures can produce runoff contour maps with regional accuracies roughly equivalent to those produced by manual methods.