Hyporheic Invertebrates Research Articles

The hyporheic zone as an invertebrate refuge during a fine sediment disturbance event

AbstractSubsurface sediments offer an important refuge that support the survival and persistence of river invertebrates during adverse surface conditions. Access to refuges for invertebrates varies with differing hydrological and substrate characteristics, especially the proportion of fine sediment. This study examines whether substrate characteristics influence the use of the hyporheic zone as an invertebrate refuge during a fine sediment disturbance event. We used 12 outdoor stream mesocosms to examine the vertical migration of benthic and hyporheic invertebrates to fine sediment loading. Each mesocosm was filled with coarse or experimentally colmated sediments. After 69 days, a fine sediment pulse of three varying fine sediment concentrations was added to the stream mesocosms. Both before and after the fine sediment pulse, a distinct gradient in the abundance and richness of hyporheic invertebrates was apparent with depth. Hyporheic abundance and taxonomic richness decreased at 5 cm and increased at 18 cm during fine sediment loading, indicating vertical migration of invertebrates from the benthic to hyporheic zone. Our study provides support for the hyporheic zone as a refuge for benthic invertebrates during fine sediment disturbance events. We also found evidence that movement pathways within subsurface sediments were still accessible and permitted bidirectional migration of individuals between the benthic and hyporheic zone in the coarse and colmated sediments during fine sediment loading. Understanding how increased fine sediment deposition affects streambed porosity will be increasingly important with ongoing climate change and anthropogenic sedimentation.

Environmental context mediates the interaction between fine sediment and hyporheic macroinvertebrate

AbstractExcessive deposition of fine‐sediment filling interstitial spaces in riverbed substrates is widely acknowledged to negatively impact the aquatic ecosystems. Hyporheic invertebrates, sensitive to ecological status, respond to the clogged substratum through more intense bioturbation. To better understand the interaction between hyporheic macroinvertebrates and fine sediment, a continuum of a naturally increasing fine‐sediment content in the Weihe River was investigated through field sampling in four seasons. Nonmetric multidimensional scaling (NMDS) and cluster analysis were employed to assess the distribution and the homogeneity in the composition variation of macroinvertebrate assemblages. Canonical correspondence analysis (CCA) was performed to reveal the context‐dependent relevance of bioturbation activity with bioturbation potential value. Our results suggest that the impact of fine‐sediment clogging on community composition and bioturbation activity was seasonally dependent due to the variability of environmental factors, such as flood events and water quality. The highest abundance and bioturbation activity occurred at moderately clogged sampling sites, while reductions in richness and bioturbation activity were observed at heavily clogged sampling sites, and the samples collected at some of the heavily clogged sites downstream did not even contain macroinvertebrates. The results indicated that the interaction between organisms and fine sediments is limited due to the complexity of the benthic and hyporheic zone. The study highlights the feasibility of hyporheic macroinvertebrates as indicators for the effects of fine‐sediment loading pressures on lotic ecosystems and the necessity of reach‐specific conservation and management strategies, especially in the downstream.

Invertebrate and Microbial Response to Hyporheic Restoration of an Urban Stream

All cities face complex challenges managing urban stormwater while also protecting urban water bodies. Green stormwater infrastructure and process-based restoration offer alternative strategies that prioritize watershed connectivity. We report on a new urban floodplain restoration technique being tested in the City of Seattle, USA: an engineered hyporheic zone. The hyporheic zone has long been an overlooked component in floodplain restoration. Yet this subsurface area offers enormous potential for stormwater amelioration and is a critical component of healthy streams. From 2014 to 2017, we measured hyporheic temperature, nutrients, and microbial and invertebrate communities at three paired stream reaches with and without hyporheic restoration. At two of the three pairs, water temperature was significantly lower at the restored reach, while dissolved organic carbon and microbial metabolism were higher. Hyporheic invertebrate density and taxa richness were significantly higher across all three restored reaches. These are some of the first quantified responses of hyporheic biological communities to restoration. Our results complement earlier reports of enhanced hydrologic and chemical functioning of the engineered hyporheic zone. Together, this research demonstrates that incorporation of hyporheic design elements in floodplain restoration can enhance temperature moderation, habitat diversity, contaminant filtration, and the biological health of urban streams.

Stable isotope ratios of emergent adult aquatic insects can be used as indicators of water pollution in the hyporheic food web

Bio-assessment protocols for the subsurface domain of river channels (i.e. hyporheic zone) are scarce despite of the known importance of its ecological function in river ecosystems. The larvae of the Alloperla ishikariana Plecoptera species inhabit the hyporheic zone. Therefore, we examined whether emergent adult A. ishikariana could serve as proxy indicators of the effects of pollution in the hyporheic food web. The study site comprised a 15-km stretch of a gravel bed river in Hokkaido, Japan, from which all invertebrates were collected from the riverbed at a depth of 30–50 cm, and emergent A. ishikariana adults were sampled in riparian zones. Water quality changed gradually along the river owing to the effects of a wastewater treatment plant and surrounding land uses. Nitrogen and carbon stable isotope ratios (SIRs) of epilithic biofilms, hyporheic particulate organic matter (POM), benthic POM, and invertebrates were used to determine the major basal carbon sources, the effects of water pollution on the hyporheic zone, and the trophic positions of dominant invertebrates. Generalized linear (mixed) models were used for statistical testing and modeling. Amphipoda and the larvae of A. ishikariana were considered as top predators and secondary consumers in the hyporheic food web, respectively. The observed similarity in water quality between the hyporheic and surface water suggested a large degree of hydrological exchange between the two zones, and resulted in positive increases in the nitrogen SIRs of hyporheic invertebrates, including A. ishikariana larvae, in proportion to nitrate levels in the surface water. The nitrogen SIRs of A. ishikariana adults were significantly correlated with the nitrogen SIRs of their larvae within the same location (adjusted R2 = 0.78), indicating that emerged adults can provide information on the longitudinal variability of the effects of synthetic nitrogen. In contrast, the carbon SIRs of adults did not predict those of their larvae, possibly reflecting the diverse feeding habitats of larvae. Overall, we demonstrated that adult aquatic insects emerging from the hyporheic zone can be used as indirect indicators of pollution-associated nutrient assimilation as well as the spatial heterogeneity of dietary carbon resources in hyporheic food web.

Investigating invertebrate biodiversity around large wood: taxonomic vs functional metrics

Large wood is a key component of river channels that affects numerous hydrological, physical and geomorphological processes. It promotes a diversity of benthic habitats in-channel and has shown to support more abundant and diverse benthic macroinvertebrate assemblages in previous ecological studies. However, the effects of large wood on the structural and functional diversities of hyporheic invertebrates are less well studied, and simultaneous examination of these diversity metrics on hyporheic and benthic compartments of the stream bed has not been conducted previously. Therefore, this study investigates the taxonomic and functional diversities of hyporheic and benthic invertebrate assemblages around natural accumulations of large wood in a British lowland river. Taxonomic and functional diversities were partitioned (into alpha, beta, and gamma diversities) and examined in reaches with and without large wood (control). We found that functional diversity is often decoupled from taxonomic diversity, demonstrating a functional redundancy of the macroinvertebrate assemblage for both hyporheic and benthic zones. Moreover, the highest functional variability at alpha-scale was observed in large wood habitats, which suggests that taxonomic diversity is enhanced by the small-scale environmental heterogeneity around large wood. To this end, this study contributes empirical evidence of functional and structural responses of invertebrates to large wood accumulation. Such information could be used to better understand the ecological implications of restoration works in lowland rivers and guide more effective management strategies.

Functional traits of hyporheic and benthic invertebrates reveal importance of wood‐driven geomorphological processes in rivers

Abstract Large wood (LW) is a natural element of river environments and an integral component of many river restoration schemes to promote biodiversity. It is an important habitat in itself, but it also induces a wide range of hydraulic, hydrological, geomorphological and chemical conditions that influence the ecological community. However, the effects of hydro‐geomorphological processes induced by LW on local benthic and hyporheic invertebrates have not been well characterized. A functional approach was applied to invertebrate data collected in a field survey at sites with LW and without LW (control) to investigate the response of hyporheic and benthic invertebrates' trait profiles in response to local LW‐induced processes. We hypothesized LW sites to be associated with different trait modalities than control sites in relation to wood‐induced processes and conditions (i.e., hyporheic exchange flow, oxygen availability, temporal stability, organic matter, denitrification, hydraulic conductivity). Multivariate analyses and partial least squares (PLS) path modelling were used to detect the differences in trait profiles between LW and control sites and to study the variation of traits as a function of hydrological, sedimentological, physical and chemical variables. Biological (i.e., aquatic stages, reproduction), physiological (i.e., dispersal, feeding habits) and behavioural (i.e., substrate preferences) trait utilization by the hyporheic meiofauna differed between LW and control sites. At LW sites, the hyporheic meiofaunal assemblage was significantly associated with aquatic active dispersal, aquatic eggs and hard substrate preferences. This trait category selection was linked to changes in physical–sedimentological processes at LW sites when compared to control sites. Macrofaunal benthic and hyporheic functional traits did not differ significantly between wood and control sites, suggesting similar functioning of these assemblages at the surface–subsurface interface. This study found that LW affects invertebrate traits by altering fluvial processes to produce, locally, a mosaic of habitats. Hyporheic meiofauna trait responses to LW processes have suggested (a) the crucial role of LW in supporting river benthic zone functioning and thus (b) a possible benefit to river restoration by enhancing functional interactions among different ecological niches. A free Plain Language Summary can be found within the Supporting Information of this article.

The impacts of cattle access to headwater streams on hyporheic zones

The hyporheic zone is an important ecotone occupying the interface between surface and ground water bodies, providing a range of important ecosystem services such as biochemical cycling, temperature regulation and downstream flood attenuation. Despite its importance in freshwater ecosystems in terms of services provided, the hyporheic zone has often been overlooked as a research topic. This study assessed the impact of cattle access to headwater streams on hyporheic zone parameters. The results indicate increases in levels of interstitial, hyporheic fine sediment downstream of cattle access points and the potential for this to negatively affect hyporheic invertebrate communities. Invertebrate community composition changes were observed at some sites with changes representing a shift to less diverse communities of smaller bodied invertebrates. The results presented here should help inform water resources managers and encourage them to consider the hyporheic zone as a part of an integrated freshwater ecosystem.

In this Issue

i DOI: https://doi.org/10.3318/BIOE.2019.05 Biology and Environment: Proceedings of the Royal Irish Academy,Vol. 119, No. 1, i–ii (2019). © Royal Irish Academy Cite as follows: Osborne, B. 2019 Editorial / In this Issue. Biology and Environment: Proceedings of the Royal Irish Academy 2019. DOI: 10.33318/ BIOE.2019.05 EDITORIAL Bruce Osborne Despite the challenging times we live in with an­ ever-increasing number of journals plying for ­ papers in the biological and environmental areas,I am pleased to say that Biology and Environment is maintaining our impact factor above 0.65 (0.676). Whilst this is the good news,maintaining or even increasing our impact factor in the future is a significant challenge so we need to continue to ensure that we receive high-quality submissions.As editor a particular onus is placed on me, together with the other members of the editorial board, to ensure that this happens. We are, however, always open to new ideas and new publication initiatives that will increase the journal’s impact and readership and I would encourage, in particular, suggestions for new Praeger Reviews and special issues. In terms of new initiatives this issue contains the first of what I hope will be a series of so-called ‘data papers’.This initiative is based on the increasing body of numerical information that is often not suitable for more conventional publications as it is not specifically hypothesis-driven research. Nevertheless , well-documented metadata is an important and often essential resource for informing current and future research as well as providing the basis for wider collaborative initiatives. Moreover, these publications provide a way of recognising all those who contributed to the collection, management and curation of the data sets. I hope, therefore, that this is a publication opportunity that a number of you can take advantage of in the future. I would like finally to recognise all the Royal Irish Academy staff, editorial board members and reviewers who have contributed to Biology and Environment over the past year. Bruce Osborne IN THIS ISSUE Limestone lake crusts Limestone lakes are often characterised by a benthos consisting of charophyte algae and a microbial crust comprising of a range of microbes intermixed with inorganic minerals.Whilst the more visible charophyte beds have received considerable attention much less is known about the functional significance and formation of the microbial crusts. Doddy et al., in this issue point out that although these crusts are sometimes considered as largely inert inorganic minerals,they are complex substrates containing a diverse assemblage of living microorganisms. Both filamentous and coccoid cyanobacteria are present as are chlorophytes and diatoms that reflect, in part, the organisms present in the water column.As expected the crusts contain a high proportion of mineral particles that may be cemented together through the actions of filamentous cyanobacteria.In terms of the controls over crust formation Doddy et al. provide evidence that this is related to P availability, with crust deterioration evident at high water column P concentrations . Crusts may also act as a significant sink for P so that conservation of these habitats should consider any effects that impact on their functionality, including increased turbidity and modifications in water chemistry. Importantly, as improvements in water column quality may not be synonymous with improvements in the status of the microbial crusts, specific conservation measures are likely to be required that are targeted directly at the benthic community. Cattle impacts on the hyporheic zone The word hyporheic, from the Greek hypo (below) and rheos (flow), was first coined by the Romanian hydrobiologist Traian Orghidan in 1955 to denote the area below the stream bed where mixing of surface and ground water occurs.This is an important interface often characterised by a unique assemblage of organisms that control the exchange of organic material, water and nutrients between surface and ground water bodies. Importantly this zone can be strongly impacted by agricultural activity, as­ O’Sullivan et al., in this issue, show.The authors detail how cattle access to the shallow areas associated with headwater streams can increase downstream sediment flow and negatively impact on hyporheic invertebrate communities. In some cases this also resulted in a reduction...

In this Issue

i DOI: https://doi.org/10.3318/BIOE.2019.05 Biology and Environment: Proceedings of the Royal Irish Academy,Vol. 119, No. 1, i–ii (2019). © Royal Irish Academy Cite as follows: Osborne, B. 2019 Editorial / In this Issue. Biology and Environment: Proceedings of the Royal Irish Academy 2019. DOI: 10.33318/ BIOE.2019.05 EDITORIAL Bruce Osborne Despite the challenging times we live in with an­ ever-increasing number of journals plying for ­ papers in the biological and environmental areas,I am pleased to say that Biology and Environment is maintaining our impact factor above 0.65 (0.676). Whilst this is the good news,maintaining or even increasing our impact factor in the future is a significant challenge so we need to continue to ensure that we receive high-quality submissions.As editor a particular onus is placed on me, together with the other members of the editorial board, to ensure that this happens. We are, however, always open to new ideas and new publication initiatives that will increase the journal’s impact and readership and I would encourage, in particular, suggestions for new Praeger Reviews and special issues. In terms of new initiatives this issue contains the first of what I hope will be a series of so-called ‘data papers’.This initiative is based on the increasing body of numerical information that is often not suitable for more conventional publications as it is not specifically hypothesis-driven research. Nevertheless , well-documented metadata is an important and often essential resource for informing current and future research as well as providing the basis for wider collaborative initiatives. Moreover, these publications provide a way of recognising all those who contributed to the collection, management and curation of the data sets. I hope, therefore, that this is a publication opportunity that a number of you can take advantage of in the future. I would like finally to recognise all the Royal Irish Academy staff, editorial board members and reviewers who have contributed to Biology and Environment over the past year. Bruce Osborne IN THIS ISSUE Limestone lake crusts Limestone lakes are often characterised by a benthos consisting of charophyte algae and a microbial crust comprising of a range of microbes intermixed with inorganic minerals.Whilst the more visible charophyte beds have received considerable attention much less is known about the functional significance and formation of the microbial crusts. Doddy et al., in this issue point out that although these crusts are sometimes considered as largely inert inorganic minerals,they are complex substrates containing a diverse assemblage of living microorganisms. Both filamentous and coccoid cyanobacteria are present as are chlorophytes and diatoms that reflect, in part, the organisms present in the water column.As expected the crusts contain a high proportion of mineral particles that may be cemented together through the actions of filamentous cyanobacteria.In terms of the controls over crust formation Doddy et al. provide evidence that this is related to P availability, with crust deterioration evident at high water column P concentrations . Crusts may also act as a significant sink for P so that conservation of these habitats should consider any effects that impact on their functionality, including increased turbidity and modifications in water chemistry. Importantly, as improvements in water column quality may not be synonymous with improvements in the status of the microbial crusts, specific conservation measures are likely to be required that are targeted directly at the benthic community. Cattle impacts on the hyporheic zone The word hyporheic, from the Greek hypo (below) and rheos (flow), was first coined by the Romanian hydrobiologist Traian Orghidan in 1955 to denote the area below the stream bed where mixing of surface and ground water occurs.This is an important interface often characterised by a unique assemblage of organisms that control the exchange of organic material, water and nutrients between surface and ground water bodies. Importantly this zone can be strongly impacted by agricultural activity, as­ O’Sullivan et al., in this issue, show.The authors detail how cattle access to the shallow areas associated with headwater streams can increase downstream sediment flow and negatively impact on hyporheic invertebrate communities. In some cases this also resulted in a reduction...

The impacts of cattle access to headwater streams on hyporheic zones

The hyporheic zone is an important ecotone occupying the interface between surface and ground water bodies, providing a range of important ecosystem services such as biochemical cycling, temperature regulation and downstream flood attenuation. Despite its importance in freshwater ecosystems in terms of services provided, the hyporheic zone has often been overlooked as a research topic. This study assessed the impact of cattle access to headwater streams on hyporheic zone parameters. The results indicate increases in levels of interstitial, hyporheic fine sediment downstream of cattle access points and the potential for this to negatively affect hyporheic invertebrate communities. Invertebrate community composition changes were observed at some sites with changes representing a shift to less diverse communities of smaller bodied invertebrates. The results presented here should help inform water resources managers and encourage them to consider the hyporheic zone as a part of an integrated freshwater ecosystem.

Effects of urban wastewater on hyporheic habitat and invertebrates in Mediterranean streams

Wastewater discharges into fluvial ecosystems represent a significant and continuous source of fine particles and nutrients that can severely modify stream community composition and functionality. Depending on both wastewater and stream features (e.g., nutrient removal treatments and stream dilution capacity), the ecological effects can be more or less severe. To determine how hyporheic habitat and hyporheos are affected, we analysed eight Mediterranean streams both upstream and downstream of a wastewater effluent. The results demonstrated that environmental factors associated with clogging, such as the quantity of fine particulate and organic matter in sediment, were magnified downstream of the wastewater inputs. Likewise, dissolved nutrients also increased but depended to a greater extent on the presence of a wastewater treatment plant and on the nitrogen and phosphorus removal treatments. The hyporheic invertebrates were more affected by clogging than by eutrophication. Both richness and diversity parameters were negatively correlated with clogging features but were not correlated with eutrophication. The most affected taxa were Macrocrustaceans, Hydrachnidia and several insect species, which decreased or were not detected downstream of the effluents. On the contrary, other taxa such as Naididae (Oligochaeta), Orthocladiinae (Chironomidae) and Potamopyrgus antipodarum (Gastropoda) benefited from the wastewater inputs.

Helophyte impacts on the response of hyporheic invertebrate communities to inundation events in intermittent streams

AbstractThe effects of experimental inundation on invertebrate communities in artificial flumes fed with treated wastewater were investigated. Flumes, designed to simulate intermittent river conditions, were planted with 3 species of helophytes widely used in river restoration around the water‐stressed regions of Europe. Different species of vegetation had different capabilities to reduce the invertebrate's negative reaction to inundation, related mostly to rhizosphere density. Of the 3 helophyte species tested, only 1, Lysimachia vulgaris, showed significant capabilities to reduce invertebrate negative reaction on inundation. Species richness of invertebrates before and after the inundation did not change in any of the flumes, whereas species density significantly declined in all flumes except one planted with L. vulgaris. This helophyte species was associated with high densities of the Culicidae larvae (common mosquitos), which has severe implications for river restoration and vector management in the region. This study indicates that the selection and establishment of different helophyte species will impact invertebrate communities in restored streams, especially streams experiencing variable inundation conditions.

Benthic and hyporheic macroinvertebrate distribution within the heads and tails of riffles during baseflow conditions

The distribution of lotic fauna is widely acknowledged to be patchy reflecting the interaction between biotic and abiotic factors. In an in situ field study, the distribution of benthic and hyporheic invertebrates in the heads (downwelling) and tails (upwelling) of riffles were examined during stable baseflow conditions. Riffle heads were found to contain a greater proportion of interstitial fine sediment than riffle tails. Significant differences in the composition of benthic communities were associated with the amount of fine sediment. Riffle tail habitats supported a greater abundance and diversity of invertebrates sensitive to fine sediment such as EPT taxa. Shredder feeding taxa were more abundant in riffle heads suggesting greater availability of organic matter. In contrast, no significant differences in the hyporheic community were recorded between riffle heads and tails. We hypothesise that clogging of hyporheic interstices with fine sediments may have resulted in the homogenisation of the invertebrate community by limiting faunal movement into the hyporheic zone at both the riffle heads and tails. The results suggest that vertical hydrological exchange significantly influences the distribution of fine sediment and macroinvertebrate communities at the riffle scale.

Characterization of the density and body size of a Gammarus pulex (Crustacea: Amphipoda) population in subsurface sediments reflects the sampling technique used

The hyporheic zone and its invertebrate fauna play vital roles in the functioning of lotic ecosystems. However, although sampling invertebrates from subsurface sediments is recognized as challenging, few studies have quantified the effectiveness of common sampling techniques. We conducted laboratory experiments to compare two common, semi-quantitative pump-sampling techniques—Bou–Rouch and vacuum-pump sampling. We determined the proportion of a Gammarus pulex (Crustacea: Amphipoda) population sampled by each method in five sediment treatments comprising coarse (16–32 mm), medium (8–16 mm), and fine (4–8 mm) gravel and combinations thereof. We compared the body size of individuals sampled and not sampled by each technique to the population mean. Density estimates obtained using both methods were low: 33 ± 5 and 5 ± 1% of the population present for Bou–Rouch and vacuum-pump samples, respectively. Density estimates were significantly higher for Bou–Rouch than for vacuum-pump samples in four sediment treatments, but were comparable in coarse gravel. The body size of organisms captured by the Bou–Rouch technique was comparable to the population mean, whereas those in vacuum-pump samples were smaller. With hyporheic invertebrates suggested as future biomonitors of ecosystem health, we recommend Bou–Rouch sampling as the more effective pump-sampling method for community characterization.

Influence of groundwater chemistry on hyporheic invertebrate assemblages is revealed by fine-scale sampling

Influence of groundwater chemistry on hyporheic invertebrate assemblages is revealed by fine-scale sampling

Influence of groundwater chemistry on hyporheic invertebrate assemblages is revealed by fine-scale sampling

Influence of groundwater chemistry on hyporheic invertebrate assemblages is revealed by fine-scale sampling

Hyporheic invertebrate assemblages at reach scale in a Neotropical stream in Brazil.

In the Neotropical Region, information concerning hyporheic communities is virtually non-existent. We carried out a sampling survey in the hyporheic zone of the Tijuca River, in the Tijuca National Park, located in the urban area of the city of Rio de Janeiro. Biological samples from the hyporheic zone were collected in three different stream reaches, in June 2012. The main objectives were: 1) to describe the structure of invertebrate assemblages in the hyporheic zone of a neotropical stream; 2) to apply a reach-scale approach in order to investigate spatial patterns of the hyporheic assemblages in relation to hydrology, depth and microhabitat typology. A total of 1460 individuals were collected and identified in 31 taxa belonging to Nematoda, Annelida, Crustacea, Hydrachnidia and Insecta. The class Insecta dominated the upper layer of the hyporheic zone. Copepods were the most abundant taxon among crustaceans and occurred mostly in the upwelling areas of the reaches. The results of this study represent one of the few contributions so far about hyporheic invertebrate assemblages of the Neotropical Region.

Changes in invertebrate assemblage composition in benthic and hyporheic zones during a severe supraseasonal drought

AbstractDroughts are unpredictable disturbances characterized in streams by declining flow, reduced habitat availability, and deteriorating abiotic conditions. Such events typically reduce benthic invertebrate taxon richness and modify assemblage composition, but little is known about how hyporheic invertebrate assemblages respond to drought or how these responses relate to changes in benthic assemblages. We hypothesized that taxon richness (α diversity) and variability (as within-site β diversity) in benthic assemblage composition would decline as drought proceeded, whereas concurrent changes in hyporheic assemblages would be lower in this more stable environment. We predicted that benthic assemblage composition between sites would converge as epigean taxa were selectively eliminated, whereas between-site hyporheic β diversity would change little. We sampled benthic and hyporheic invertebrates concurrently from 4 sites along a groundwater-fed stream during the final stages of a severe supraseasonal droug...

The effects of increased flow and fine sediment on hyporheic invertebrates and nutrients in stream mesocosms

Summary River regulation and altered land use are two common anthropogenic disturbances in rivers worldwide. Alteration of the stream bed, through processes such as siltation, or of hydrology through river regulation, are likely to modify hyporheic processes or clog interstitial space and thereby affect both hyporheic invertebrates and nutrient dynamics. We tested the separate and combined effects of increased flow and increased fine sediment on hyporheic water quality and invertebrates in flume mesocosms. Each mesocosm contained two bed sediment types: clean sediment in the upstream section and experimentally colmated (EC) sediment (10% by weight of fine sediment) in the downstream section. Two flow rates were established, a higher flow rate to create turbulent flow in six mesocosms and a lower flow rate to create a transitional flow between turbulent and laminar flows in the remaining six mesocosms. Invertebrates and physicochemistry were sampled after 30 days at three depths (5, 11 and 18 cm), and the flows in six of twelve mesocosms were switched. The experiment was concluded after sampling invertebrates and physicochemistry on day 70. The addition of fine sediment to the mesocosm bed generally increased ammonium and decreased nitrate and soluble reactive phosphorus concentrations, decreased oxygen penetration and altered invertebrate assemblage structure. Increased flow rates generally lowered ammonium concentrations, increased soluble reactive phosphorus concentrations, increased oxygen penetration and altered invertebrate assemblage structure. Our hypothesis that higher flows would ameliorate any effects of added fine sediment was generally supported for oxygen penetration and nitrate concentration. However, we observed no differences in interaction effects of flow regime and sediment type either on other nutrient concentrations or invertebrate assemblage structure. The rates of flow used in our mesocosms did not appear to reach the threshold required to remove fine sediment. It is generally recognised that river hyporheic restoration requires a set of objectives against which the outcomes can be measured yet this is often overlooked. Our research provides preliminary guidelines that small amounts of fine sediment can have deleterious ecological effects. However, further research is required to evaluate whether lower percentages of bed fine sediment result in ecological impairment and to determine what flow rates are required to ameliorate colmation impacts.

The influence of water quality on hyporheic invertebrate communities in agricultural catchments

Despite knowing that agricultural practices affect river ecosystems, studies on water quality and associated hyporheic invertebrate communities are rare. Yet such knowledge is essential for sustainable use of agricultural and water resources. This study, carried out in the agricultural region of south-eastern Ireland in Spring 2007, examined the effect of water pollution on hyporheic fauna. Six river sites of known water quality were assigned to two treatments, namely, clean and polluted rivers. Two hyporheic habitats, below the wetted channel (hyporheic substream) and below the exposed gravel bank (parafluvial), were sampled within each treatment. Total invertebrate densities and richness, crustacean densities and richness, and densities of Ephemeroptera, Plecoptera and Trichoptera (EPT) were significantly reduced in polluted hyporheic and parafluvial habitats. A higher recorded concentration of nitrate in the polluted hyporheic substream habitats was a significant factor in determining the invertebrate assemblages, with reductions in total and crustacean densities, and EPT richness. Similarly, invertebrate density and richness were reduced in polluted parafluvial habitats, likely being related to agricultural intensity, management practices and reduced riparian buffering. This study highlights the direct effects of agricultural practices on the invertebrate communities of hyporheic habitats and emphasises the need for holistic management and conservation measures to ensure future protection.