Phosphorus retention in a lowland Neotropical stream following an eight-year enrichment experiment

Human alteration of the global P cycle has led to widespread P loading in freshwater ecosystems. Much research has been devoted to the capacity of wetlands and lakes to serve as long-term sinks for P inputs from the watershed, but we know much less about the potential of headwater streams to serve in this role. We assessed storage and retention of P in biotic and abiotic compartments after an 8-y experimental P addition to a 1st-order stream in a Neotropical wet forest. Sediment P extractions indicated that nearly all P storage was in the form of Fe- and Al-bound P (∼700 μg P/g dry sediment), similar to nearby naturally high-P streams. At the end of the enrichment, ∼25% of the total P added over the 8-y study was still present in sediments within 200 m of the injection site, consistent with water-column measurements showing sustained levels of high net P uptake throughout the experiment. Sediment P declined to baseline levels (∼100 μg P/g dry sediment) over 4 y after the enrichment ended. Leaf-litter P content increased nearly 2× over background levels during P enrichment and was associated with a 3× increase in microbial respiration rates, although these biotic responses were low compared to nearby naturally high- P streams. Biotic storage accounted for \u3c0.03% of retention of the added P. Our results suggest that the high sorption capacity of these sediments dampened the biotic effects of P loading and altered the timing and quantity of P exported downstream

Evidence of American Martens Populating the Turtle Mountains of North Dakota

American martens (Martes americana) were native to northeastern North Dakota but were considered extirpated by the early 1800s. Although there is no historic evidence of martens occurring beyond the northeast, forested habitat potentially suitable for martens exists in the Turtle Mountains region of northcentral North Dakota and southwestern Manitoba. From 1989– 1991, the Turtle Mountain Trappers Association translocated 59 martens into the Canadian portion of the Turtle Mountains. During summer 2007, we used covered track-plates and/or remotely-triggered cameras placed at 123 survey sites distributed among 41 1-km2 grid cells (a GIS-generated layer imposed on electronic maps of the study region) to determine if martens occupied the Turtle Mountains in North Dakota. Martens were detected at 26 (21%) sites, representing 20 of the 41 sample cells (49%) widely dispersed throughout the study area. Our study provided the first evidence of martens occurring in North Dakota since the early 1800s

On the Portability of Prolog Applications

The non-portability of Prolog programs is widely considered one of the main problems facing Prolog programmers. Although since 1995, the core of the language is covered by the ISO standard 13211-1, this standard has not been sufficient to support large Prolog applications. As an approach to address this problem, since 2007, YAP and SWI-Prolog have established a basic compatibility framework. The aim of the framework is running the same code on Edinburgh-based Prolog systems rather than having to migrate an application. This article describes the implementation and evaluates this framework by studying how it can be used on a number of libraries and an important application. © 2011 Springer-Verlag

Retention time and dispersion associated with submerged aquatic canopies

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 43 (2007): W04422, doi:10.1029/2006WR005362.The shear layer at the top of a submerged canopy generates coherent vortices that control exchange between the canopy and the overflowing water. Unlike free shear layers, the vortices in a canopy shear layer do not grow continuously downstream but reach and maintain a finite scale determined by a balance between shear production and canopy dissipation. This balance defines the length scale of vortex penetration into the canopy, δ e , and the region of rapid exchange between the canopy and overflow. Deeper within the canopy, transport is constrained by smaller turbulence scales. A two-box canopy model is proposed on the basis of the length scale δ e . Using diffusivity and exchange rates defined in previous studies, the model predicts the timescale required to flush the canopy through vertical exchange over a range of canopy density and height. The predicted canopy retention times, which range from minutes to an hour, are consistent with canopy retention inferred from tracer observations in the field and comparable to retention times for some hyporheic regions. The timescale for vertical exchange, along with the in-canopy velocity, determines the minimum canopy length for which vertical exchange dominates water renewal. Shorter canopies renew interior water through longitudinal advection. Finally, canopy water retention influences longitudinal dispersion through a transient storage process. When vertical exchange controls canopy retention, the transient storage dispersion increases with canopy height. When longitudinal advection controls water renewal, dispersion increases with canopy patch length.This material is based upon work supported by the National Science Foundation under grant EAR0309188

Fine-Scale in Situ Measurement of Riverbed Nitrate Production and Consumption in an Armored Permeable Riverbed

Alteration of the global nitrogen cycle by man has increased nitrogen loading in waterways considerably, often with harmful consequences for aquatic ecosystems. Dynamic redox conditions within riverbeds support a variety of nitrogen transformations, some of which can attenuate this burden. In reality, however, assessing the importance of processes besides perhaps denitrification is difficult, due to a sparseness of data, especially in situ, where sediment structure and hydrologic pathways are intact. Here we show in situ within a permeable riverbed, through injections of 15N-labeled substrates, that nitrate can be either consumed through denitrification or produced through nitrification, at a previously unresolved fine (centimeter) scale. Nitrification and denitrification occupy different niches in the riverbed, with denitrification occurring across a broad chemical gradient while nitrification is restricted to more oxic sediments. The narrow niche width for nitrification is in effect a break point, with the switch from activity “on” to activity “off” regulated by interactions between subsurface chemistry and hydrology. Although maxima for denitrification and nitrification occur at opposing ends of a chemical gradient, high potentials for both nitrate production and consumption can overlap when groundwater upwelling is strong