Despite a developing literature on urban streams, few studies have addressed the timing and mechanisms of urban-induced stream hydrogeomorphic adjustment on biotic assemblages. Here, we investigated ...the relationships between urbanization-driven annual changes in fluvial geomorphic characteristics and fish assemblages in 12 headwater streams in the Columbus Metropolitan Area (CMA), Ohio (USA) over 3-5 years. Multiple stream hydrogeomorphic characteristics changed over time including slope (0.1% decrease on average), discharge (39% decrease), and shear stress (29% decrease), some in concert with one another (e.g., slope and shear stress). Species-specific fish associations with hydrogeomorphic associations varied in nature and strength by year and thus were somewhat equivocal. At the assemblage level, we observed a negative relationship between D.sub.50 (median sediment particle size) and % tolerant individuals as well as a positive trend between incision ratio and % generalists over study years. Study reaches with higher total catchment imperviousness were associated with both finer median sediment size (R.sup.2 = 0.19) and lower assemblage diversity (R.sup.2 = 0.55). These results contribute to current understanding of the drivers of fish assemblages in urbanizing catchments, and point to urban-induced hydrogeomorphic alterations as one mechanism through which land-use changes influence in-channel characteristics important to aquatic biota.
Urbanization in stream catchments can have strong effects on stream channel hydrogeomorphic features including channel dimensions, channel-floodplain connectivity, and flood regime. However, the ...consequences of hydrogeomorphic alterations on aquatic-terrestrial subsidy dynamics are largely unexplored. We examined the associations among hydrogeomorphic characteristics, emergent aquatic insect assemblages, and the density and trophic dynamics of riparian spiders of the family Tetragnathidae at 23 small urban stream reaches in the Columbus, OH (United States) Metropolitan Area. Naturally abundant stable isotopes of
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C and
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N were used to quantify the relative contribution of aquatically derived energy (i.e., nutritional pathways deriving from algae) to tetragnathid spiders and their trophic position. Bankfull discharge was negatively related to both emergence rate and family richness. On average, tetragnathid spiders relied on aquatically derived energy for 36% of their nutrition, with the greatest reliance found for spiders next to channels with wider flood-prone widths and proportionally fewer emergent insects of the family Chironomidae. Mean emergent aquatic insect reliance on aquatically derived energy was 32% and explained 44% of the variation in tetragnathid aquatically derived energy. A positive relationship between δ
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C of tetragnathid spiders and emergent insects provides additional evidence of tetragnathid reliance on emergent insects. Mean tetragnathid trophic position was 2.85 and was positively associated with channel sinuosity and negatively associated with aquatic insect emergence rate. Sinuosity was also positively related to aquatically derived energy of emergent aquatic insects; as well as emergent insect family richness; % Ephemeroptera, Plecoptera, and Trichoptera (EPT); and aquatic insect emergence rate; implicating instream habitat-mediated shifts in emergent aquatic insect communities as an indirect mechanistic link between hydrogeomorphic processes and spiders. Our findings underscore that the impacts of stream hydrogeomorphic alterations can cascade into terrestrial food webs. These results suggest that monitoring and restoration of fluvial geomorphic form and function (e.g., sinuosity, slope, and hydrology) confer benefits to both aquatic and terrestrial riparian ecosystems in urban catchments.
Summary
Evaluating the biological integrity of stream ecosystems requires a clear understanding of biological responses to anthropogenic stressors. Co‐variation of stressors with natural landscape ...gradients has been shown to complicate the ability of biological assessments to detect community‐level responses to anthropogenic stressors. Similarly, the co‐varying occurrence of non‐native species would also likely confound the ability of biological assessments to accurately determine biological integrity, although these relationships have been less studied.
We compared fish communities in 99 wadeable tributaries (with catchments of 10–35 km2) of the upper Allegheny River watershed, Pennsylvania, U.S.A., to disentangle the effects of human‐induced stressors associated with agricultural development, the presence of non‐native brown trout (Salmo trutta) and background variation in community composition associated with natural landscape features.
Multivariate analyses using both taxonomic and trait‐based data revealed that environmental gradients sorted fish species into different thermal communities (coolwater versus warmwater). Layered over the shift in thermal communities was the presence of large‐bodied (piscivorous) brown trout, which along with agricultural land use, was a consistent determinant of community diversity and presence–absence of nine common native species. Small‐bodied taxa (minnows, darters) were the most responsive to the presence of these large non‐native predators.
Our results highlight how the presence of a non‐native species can modify the interactions between natural and anthropogenic stressor gradients and therefore confound the ability to detect signals between land use stressors and local stream community composition. The complicated interaction between brown trout and other anthropogenic stressors documented herein is likely to be a widespread phenomenon given the global introductions of many salmonid species into systems with varying anthropogenic stressor gradients. Overall, understanding how non‐native species influence stream community composition should lead to biological assessments with greater capabilities for detecting non‐native effects on biological integrity relative to the more frequently evaluated land use stressors.
A technique for time and frequency transfer over an asynchronous fiber optical transmission control protocol (TCP)/IP network is being developed in Sweden by SP Measurement Technology together with ...STUPI. The technique is based on passive listening to existing data traffic at 10 Gb/s in the network. Since the network is asynchronous, intermediate supporting clocks will be located and compared at each router. We detect, with a specially designed high-speed optoelectronic device, a header recognizer, the frame alignment bytes of the synchronous optical network (SONET)/synchronous digital hierarchy (SDH) protocol, as a reference for the supporting clock comparison. The goal of the project is to establish a time transfer system with an accuracy on the nanosecond level. In this paper, we present the results of a time transfer over a distance of 5 km. We have compared two clocks: a cesium clock at the Swedish National Laboratory for time and frequency and a remote rubidium clock. The results of the time transfer with the fiber link have been simultaneously compared to measurements with a Global Positioning System (GPS) carrier phase link in terms of precision and stability. The root-mean-square (rms) difference between the time difference measured with the fiber link and the GPS link is approximately 300 ps. A large part of the difference is due to the heating of the GPS antenna cable, which introduces daily delay variations on the order of 1 ns from peak to peak. For one of the days with small day-to-day variations in temperature, the corresponding rms difference is 72 ps, and the Allan deviation is below 30 ps for averaging times longer than 5 min.
A nationwide system for accurate time distribution is being developed, utilizing synchronization in an SDH-network. The first experimental results based on this technique are presented, performed on, ...but not limited to, STM-64.
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