Thresholds of lake and reservoir connectivity in river networks control nitrogen removal.

Lakes, reservoirs, and other ponded waters are ubiquitous features of the aquatic landscape, yet their cumulative role in nitrogen removal in large river basins is often unclear. Here we use predictive modeling, together with comprehensive river water quality, land use, and hydrography datasets, to examine and explain the influences of more than 18,000 ponded waters on nitrogen removal through river networks of the Northeastern United States. Thresholds in pond density where ponded waters become important features to regional nitrogen removal are identified and shown to vary according to a ponded waters' relative size, network position, and degree of connectivity to the river network, which suggests worldwide importance of these new metrics. Consideration of the interacting physical and biological factors, along with thresholds in connectivity, reveal where, why, and how much ponded waters function differently than streams in removing nitrogen, what regional water quality outcomes may result, and in what capacity management strategies could most effectively achieve desired nitrogen loading reduction.

Estimating summer nutrient concentrations in Northeastern lakes from SPARROW load predictions and modeled lake depth and volume.

Global nutrient cycles have been altered by the use of fossil fuels and fertilizers resulting in increases in nutrient loads to aquatic systems. In the United States, excess nutrients have been repeatedly reported as the primary cause of lake water quality impairments. Setting nutrient criteria that are protective of a lakes ecological condition is one common solution; however, the data required to do this are not always easily available. A useful solution for this is to combine available field data (i.e., The United States Environmental Protection Agency (USEPA) National Lake Assessment (NLA)) with average annual nutrient load models (i.e., USGS SPARROW model) to estimate summer concentrations across a large number of lakes. In this paper we use this combined approach and compare the observed total nitrogen (TN) and total phosphorus (TN) concentrations in Northeastern lakes from the 2007 National Lake Assessment to those predicted by the Northeast SPARROW model. We successfully adjusted the SPARROW predictions to the NLA observations with the use of Vollenweider equations, simple input-output models that predict nutrient concentrations in lakes based on nutrient loads and hydraulic residence time. This allows us to better predict summer concentrations of TN and TP in Northeastern lakes and ponds. On average we improved our predicted concentrations of TN and TP with Vollenweider models by 18.7% for nitrogen and 19.0% for phosphorus. These improved predictions are being used in other studies to model ecosystem services (e.g., aesthetics) and dis-services (e.g. cyanobacterial blooms) for ~18,000 lakes in the Northeastern United States.

The fate of the index metacarpophalangeal joint following pollicization.

PURPOSE: To characterize the complications that occur at the index metacarpophalangeal (MCP) joint following pollicization and to identify the blood supply of the index MCP joint. METHODS: Eighty-five pollicized digits in 74 patients (1974-2007) were followed after surgery and had documented clinical examinations and radiographs to evaluate physeal arrest, nonunion at the pollicized digit base, and instability of the new carpometacarpal joint at a minimum of 2 years following surgery. RESULTS: Proximal phalanx physeal arrest was the most common complication. Radiographic nonunion at the juncture of the index metacarpal head and base occurred with and without instability. Twenty-one of 85 pollicized digits showed radiographic evidence of physeal arrest, 12 of which were complete and 9 partial. No clinical factor was found to significantly correlate with a physeal arrest, although the 9 patients with the diagnosis of Holt-Oram syndrome trended toward a higher percentage, with 6 digits in 5 patients with Holt-Oram syndrome showing this complication. Twenty pollicized MCP joints did not have bony union to the base of the index metacarpal, but only 3 were clinically unstable and required surgical stabilization. Ten pollicized digits developed some degree of instability and subluxation at the new carpometacarpal joint, but only one required surgical intervention. In recent cases, a search for the blood supply to the MCP joint has demonstrated a consistent vessel deep to the interosseous muscles that arborizes on the volar metacarpal neck. Our surgical technique has evolved to preserve this vessel whenever possible. CONCLUSIONS: Our complications are most likely due to technical factors. Careful dissection of the index MCP joint during pollicization should help reduce physeal growth arrest. Patients with Holt-Oram syndrome might have an increased risk of growth arrest. However, the majority of patients did not require secondary surgery and have good function. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Source and Delivery of Nutrients to Receiving Waters in the Northeastern and Mid-Atlantic Regions of the United States.

This study investigates nutrient sources and transport to receiving waters, in order to provide spatially detailed information to aid water-resources managers concerned with eutrophication and nutrient management strategies. SPAtially Referenced Regressions On Watershed attributes (SPARROW) nutrient models were developed for the Northeastern and Mid-Atlantic (NE US) regions of the United States to represent source conditions for the year 2002. The model developed to examine the source and delivery of nitrogen to the estuaries of nine large rivers along the NE US Seaboard indicated that agricultural sources contribute the largest percentage (37%) of the total nitrogen load delivered to the estuaries. Point sources account for 28% while atmospheric deposition accounts for 20%. A second SPARROW model was used to examine the sources and delivery of phosphorus to lakes and reservoirs throughout the NE US. The greatest attenuation of phosphorus occurred in lakes that were large relative to the size of their watershed. Model results show that, within the NE US, aquatic decay of nutrients is quite limited on an annual basis and that we especially cannot rely on natural attenuation to remove nutrients within the larger rivers nor within lakes with large watersheds relative to the size of the lake.

The Role of Headwater Streams in Downstream Water Quality.

Knowledge of headwater influences on the water-quality and flow conditions of downstream waters is essential to water-resource management at all governmental levels; this includes recent court decisions on the jurisdiction of the Federal Clean Water Act (CWA) over upland areas that contribute to larger downstream water bodies. We review current watershed research and use a water-quality model to investigate headwater influences on downstream receiving waters. Our evaluations demonstrate the intrinsic connections of headwaters to landscape processes and downstream waters through their influence on the supply, transport, and fate of water and solutes in watersheds. Hydrological processes in headwater catchments control the recharge of subsurface water stores, flow paths, and residence times of water throughout landscapes. The dynamic coupling of hydrological and biogeochemical processes in upland streams further controls the chemical form, timing, and longitudinal distances of solute transport to downstream waters. We apply the spatially explicit, mass-balance watershed model SPARROW to consider transport and transformations of water and nutrients throughout stream networks in the northeastern United States. We simulate fluxes of nitrogen, a primary nutrient that is a water-quality concern for acidification of streams and lakes and eutrophication of coastal waters, and refine the model structure to include literature observations of nitrogen removal in streams and lakes. We quantify nitrogen transport from headwaters to downstream navigable waters, where headwaters are defined within the model as first-order, perennial streams that include flow and nitrogen contributions from smaller, intermittent and ephemeral streams. We find that first-order headwaters contribute approximately 70% of the mean-annual water volume and 65% of the nitrogen flux in second-order streams. Their contributions to mean water volume and nitrogen flux decline only marginally to about 55% and 40% in fourth- and higher-order rivers that include navigable waters and their tributaries. These results underscore the profound influence that headwater areas have on shaping downstream water quantity and water quality. The results have relevance to water-resource management and regulatory decisions and potentially broaden understanding of the spatial extent of Federal CWA jurisdiction in U.S. waters.

Factors influencing mercury in freshwater surface sediments of northeastern North America.

We report on an inventory and analysis of sediment mercury (Hg) concentrations from 579 sites across northeastern North America. Sediment Hg concentrations ranged from the limit of detection ca. 0.01-3.7 microg g(-1) (dry weight, d.w.), and the average concentration was 0.19 microg g(-1) (d.w.) Sediment methylmercury concentrations ranged from 0.15 to 21 ng g(-1) (d.w.) and the mean concentration was 3.83 ng g(-1) (d.w.). Total Hg concentrations (HgT) were greatest in lakes > reservoirs > rivers, although the proportion of Hg as methylmercury showed an inverse pattern. Total Hg was weakly and positively correlated with the sediment organic matter and percent of watershed as forested land, and weakly and negatively correlated with sediment solids content, drainage area, and agricultural land. Sediment methylmercury concentrations were weakly and positively correlated to wetland area, and weakly and negatively correlated to drainage area. Methylmercury, expressed as a percentage of HgT was positively correlated to agricultural land area. For sites with co-located sediment and fish-tissue sampling results, there was no relationship between sediment Hg and fish-tissue Hg. Finally, our data indicate that at least 44% of waters across the region have sediment HgT concentrations in excess of Canadian and United States minimum sediment contaminant guidelines for the protection of aquatic biota.

Mortality in Emergency Department Sepsis (MEDS) score: a prospectively derived and validated clinical prediction rule.

OBJECTIVES: Our objectives were a) to identify univariate correlates of death in emergency department patients at risk for infection; b) to perform multivariate analyses and identify independent predictors of death; and c) to develop and internally validate a prediction rule that may be used in the emergency department to risk stratify patients into different risk groups to predict their mortality rate. DESIGN: Prospective cohort study. SETTING: Emergency department of an urban university referral center. PATIENTS: Consecutive emergency department patients, aged 18 or older, who were at risk for infection, as indicated by the emergency department physician ordering a blood culture between February 1, 2000, and February 1, 2001. Of 3,301 eligible patient visits, 3,179 (96%) were enrolled. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The primary outcome was 28-day in-hospital mortality rate. There were 2,070 visits in the derivation set, with 110 deaths (5.3%), and 1,109 visits in the validation set, with 63 deaths (5.7%). Independent multivariate predictors of death were terminal illness (odds ratio, 6.1; 95% confidence interval, 3.6-10.2), tachypnea or hypoxia (2.7, 1.6-4.3), septic shock (2.7, 1.2-5.7), platelet count <150,000 (2.5, 1.5-4.3), band proportion >5% (2.3, 1.5-3.5), age >65 (2.2, 1.3-3.6), lower respiratory infection (1.9, 1.2-3.0), nursing home residence (1.9, 1.2-3.0), and altered mental status (1.6, 1.0-2.6). The clinical prediction rule stratified patients into mortality risk groups of very low, 0.9% (95% confidence interval, 0.2-1.5%); low, 2.0% (0.8-3.2%); moderate, 7.8% (5.6-10%); high, 20% (13-27%); and very high, 50% (36.1-64%) in the derivation set. Mortality rates for the corresponding risk groups in the validation set were 1.1%, 4.4%, 9.3%, 16%, and 39%, respectively. The receiver operating characteristic area for the rule was 0.82 in the derivation set and 0.78 in the validation set. CONCLUSIONS: In patients with suspected infection, this model identifies significant correlates of death and allows stratification of patients according to mortality risk. As new therapies become available for patients with sepsis syndromes, the ability to predict mortality risk may be helpful in triage and treatment decisions.