Contrasting responses to catchment modification among a range of functional and structural indicators of river ecosystem health

1. The value of measuring ecosystem functions in regular monitoring programs is increasingly being recognised as a potent tool for assessing river health. We measured the response of ecosystem metabolism, organic matter decomposition and strength loss, and invertebrate community composition across a gradient of catchment impairment defined by upstream landuse stress in two New Zealand streams. This was performed to determine if there were consistent responses among contrasting functional and structural indicators. 2. Rates of gross primary production (GPP) and ecosystem respiration (ER) ranged from 0.1 to 7.0 gO2 m−2 day−1 and from 0.34 to 16.5 gO2 m−2 day−1 respectively. Rates of GPP were variable across the landuse stress gradient, whereas ER increased linearly with the highest rates at the most impacted sites. Production/respiration (P/R) and net ecosystem metabolism (NEM) indicated that sites at the low and high ends of the stress gradient were heterotrophic with respiration rates presumably relying on organic matter from upstream sources, adjacent land or point sources. Sites with moderate impairment were predominantly autotrophic. 3. Declines in the tensile strength of the cotton strips showed no response across part of the gradient, but a strong response among the most impaired sites. The rate of mass loss of wooden sticks (Betula platyphylla Sukaczev) changed from a linear response to a U-shaped response across the impairment gradient after water temperature compensation, whereas leaf breakdown at a subset of sites suggested a linear loss in mass per degree-day. Three macroinvertebrate metrics describing the composition of the invertebrate community and its sensitivity to pollution showed similar linear inverse responses to the landuse stress gradient. 4. The first axis of a redundancy analysis indicated an association between landuse stress and various measures of water quality, and wooden stick mass loss, the invertebrate metric % EPT [percentage of macroinvertebrate taxa belonging to the Ephemeroptera, Plecoptera and Trichoptera (excluding Hydroptilidae] taxa, P/R and NEM, supporting the utility of these structural and functional metrics for assessing degree of landuse stress. The second axis was more strongly associated with catchment size, ER and GPP which suggests that these indicators were responding to differences in stream size. 5. Our results suggest that nonlinear responses to catchment impairment need to be considered when interpreting measurements of ecosystem function. Functional indicators could be useful for detecting relatively subtle changes where the slope of the response curve is maximised and measurements at the low and high ends of the impairment gradient are roughly equivalent. Such responses may be particularly valuable for detecting early signs of degradation at high quality sites, allowing management responses to be initiated before the degradation becomes too advanced, or for detecting initial moves away from degraded states during the early stages of restoration. Close links between structural and functional indices of river health across an impairment gradient are not necessarily expected or desirable if the aim is to minimise redundancy among ecological indicators

A Network Model for Primary Production Highlights Linkages Between Salmonid Populations and Autochthonous Resources

Spatial variation in fish densities across river networks suggests that the influence of food and habitat resources on assemblages varies greatly throughout watersheds. Conceptual models predict that in situ primary production should vary with river characteristics, but the influence of autochthonous resource availability on the capacity for river reaches to support fish is poorly understood. We estimated primary production throughout the South Fork and Middle Fork of the John Day River, Oregon, by measuring diel cycles in dissolved oxygen (DO) during July 2013. Using these data, we (1) evaluated the extent to which juvenile salmonid abundance and resource limitation correlated with areas of high gross primary production (GPP), (2) developed models to predict GPP from both site‐level measurements and remotely sensed data, and (3) made predictions of GPP across the entirety of the Middle Fork John Day River (MFJD) network and assessed the utility of these spatially continuous predictions for describing variation fish densities at broad scales. We produced reliable estimates of GPP at sites where DO loggers were deployed using measurements of solar exposure, water temperature, and conductivity measured at each site, as well as surrogates for these data estimated from remote sensing data sources. Estimates of GPP across fish sampling sites explained, on average, 58–63% of the variation in juvenile salmonid densities during the summer sampling period, and 51–83% during the fall sampling period, while continuous network predictions of GPP explained 44% of the variation in fish densities across 29 km of the MFJD. Further, GPP explained nearly half of the variation in juvenile steelhead dietary resource limitation, as inferred from bioenergetics modeling results. These results comprise a first effort at quantifying variation in autochthonous production across an entire river network and, importantly, provide a much‐needed food‐web context for guiding more effective fish and habitat management

Next-Generation Scientists Get a Taste of Their Future Careers

Article provides an overview of the middle and high school poster session that took place during the 2014 Joint Aquatic Sciences Meeting (JASM) in Portland, Oregon. The poster session provided the students with opportunity to participate in the research process and prepare their posters

Influence of Filter Feeders on Seston Availability and Quality and Resulting Longitudinal Change in Filter-Feeder Abundance and Composition

The goal of our study is to examine effects of ?lter-feeders on seston availability along a rif?e of the Susquehanna River and conversely to see if seston affects density of ?lter feeders present at different lolcations along the rif?e. We determined con

Habitat Changes in Agricultural Streams After Implementing Channel and Riparian Management

Sediment from stream bank erosion and runoff from agricultural fields can transform rocky-bottom stream channels with varying depths to silt-clogged waterways with homogeneous habitat. Physical modifications to stream banks can be used to increase water velocity and direct stream flow toward the center of the channel, which can mobilize and transport sediments and increase depth heterogeneity in streams. State agencies (PA-FBC, PA-DEP) have partnered with local organizations (NPC, county conservation districts, watershed groups) and landowners to implement stream restoration practices along a number of agricultural streams in central Pennsylvania through the Northcentral Stream Restoration Partnership. In May and June 2017, bank stabilization and flow control structures were installed along a 0.5-mile reach of Conley Run, a tributary of Rapid Run in Union County impaired by agriculture. We conducted surveys of water quality, in-stream habitat, algal biomass, benthic macroinvertebrates, and fish in a 350-m section of the restoration reach prior to restoration. We sampled Conley Run in October 2017 to quantify changes in water quality, and surveyed again in May 2018 to quantify water quality as well as stream velocity, depth, substrate characteristics, and channel shape as a result of the structural modifications to the stream. Based on data from a nearby site in Turtle Creek, we expected Conley Run to have faster velocity, more variable depth, less silt and more coarse substrates, and decreased width compared to pre-restoration conditions. We found an increase in velocity, decreased silt which is related to increased course substrate, and a decreased width, as we predicted. However, depth variability did not increase as we predicted. These changes should improve in-stream habitat conditions for biota and lead to higher diversity of invertebrates and fish. Once it becomes established, riparian vegetation along the creek should also improve shade and cover, and the new riparian buffer should help to improve water quality by reducing inputs of sediment and nutrients from nearby agricultural fields and pastures

Tributary and Mainstem Benthic Macroinvertebrate Communities Linked By Direct Dispersal and Indirect Habitat Alteration

Benthic communities in tributary-mainstem networks might interact via downstream drift of invertebrates or material from tributaries and adult dispersal from the mainstem. Depending on the strength of these interactions, mainstem downstream communities are expected to be more similar to tributary communities due to drift or habitat alteration. Communities not connected by flow are expected to be similar due to adult dispersal but decreasing in similarity with distance from the mainstem. We investigated interactions between invertebrate communities of a 7th order river and 5th order tributary by comparing benthic community structure in the river upstream and downstream of the tributary confluence and upstream in the tributary. Non-metric multidimensional scaling showed invertebrate communities and habitat traits from river locations directly downstream of the tributary clustered tightly, intermediate between tributary and mid-channel river locations. In addition, Bray-Curtis dissimilarity increased between the mainstem and tributary with distance upstream in the tributary. Our results indicate that similarities between mainstem and tributary communities are potentially caused by direct mass effects from tributary to downstream mainstem communities by invertebrate drift and indirect mass effects by habitat restructuring via material delivery from the tributary, as well as potential effects of adult dispersal from the river on proximal tributary communities