Catchment Vegetation Cover Research Articles

Long-term changes and seasonal variability in the stream macrofauna of a Himalayan river system

Interpreting long-term variability in mountain stream ecosystems is challenging where potential causes such as climate change and altered land-use act simultaneously. The scarcity of historical data also limits research opportunity, especially at low latitudes. Here we assess the macroinvertebrate fauna of 12 Himalayan streams in Nepal covering an altitudinal gradient from 1500 to 3900 m asl using data from 1992, 2022 and 2023. We aimed to: 1) compare long-term change in richness and community composition over three decades to short-term seasonal variation, and 2) analyse long-term changes in relation to catchment properties. Rarefied richness decreased equally with altitude in 1992 and 2022, but was greater at most sites in 2022, with several new families detected. In contrast, no clear seasonal pattern was found. The 2022:1992 ratio in rarefied richness was positively correlated with catchment area and weakly with maximum catchment altitude, while the two highest and glaciated sites gained relatively more taxa than other sites. NMDS ordinations from rarefied Bray-Curtis dissimilarities showed considerable overlap in communities among the three datasets. Pairwise rarefied dissimilarities among all sites increased significantly with altitudinal distance between sites in 1992 while there was no such relationship in 2022. Dissimilarities between 1992 and 2022 samples showed a near-significant correlation with increased catchment vegetation cover as shown by NDVI. Our study is the first to document long-term variations in stream macroinvertebrate communities in Himalayan mountain streams, illustrating how some altitudinal patterns have remained stable through time while others appear to have weakened with links to global change.

Temperature and palaeolake evolution during a Middle Pleistocene interglacial–glacial transition at the Palaeolithic locality of Schöningen, Germany

The Middle Pleistocene Reinsdorf sequence at the Lower Palaeolithic sites of Schöningen offers the opportunity to reconstruct a rarely well‐preserved post‐Holsteinian environmental transition from an interglacial into a glacial phase along with its highly dynamic interjacent climatic oscillations. Combining biological proxies, element composition and stable isotope ratios of two lakeshore sequences at excavation site 13 II, we demonstrate repeated variations in climate, hydrology and catchment vegetation cover. New ostracod‐based quantitative mean summer and winter air temperature reconstructions with the Mutual Ostracod Temperature Range (MOTR) method provide the first detailed information about the temperature evolution. The interglacial temperature maximum, probably corresponding to Marine Isotope Stage 9e, is followed by a first dry phase and, during the younger part of the Reinsdorf sequence, by a second dry period. Both were marked by lower precipitation/evaporation ratios, reduced vegetation cover in the catchment and increased surface inflows from springs. Temperature reconstructions of these two steppe (open woodland) phases yield very narrow ranges for mean January (−4–0 °C) and July (+17–19 or +17–21 °C) air temperatures, demonstrating that, while summers were similar to those of today, winters were at least 1 °C colder, hinting at a more pronounced continental climate. Precise temperature estimates for the interjacent woodland and steppe (woodland) phase are hindered by generally wider ranges produced by the MOTR method (January mean −4–3 °C, July mean +15–21 °C). The development of a more extensive vegetation cover, reducing surface runoff and erosion in favour of increased river and groundwater discharge, as indicated by a shift in microfossil and stable isotope records, suggests generally more humid climates with higher precipitation/evaporation ratios as well as reduced seasonal temperature variations.

Tracing climate and human-driven erosional activity in the Transylvania lowlands (Central-Eastern Europe) during the Holocene

Erosion is a complex geomorphological process controlled by climate, soil and vegetation characteristics in addition to land-use. However, the interplay of these drivers is not fully understood. Here we present a 11.8 ka multi-proxy record of geochemical, mineral magnetic and grain size analyses from Lake Stiucii, in the Transylvania lowlands (CE Europe) documenting past erosional activity and the drivers of landscape change. We identify three major phases in the site’s development. The first, a lacustrine phase (11.8–10.9 cal ka BP), is characterised by open water conditions with significant river inflow and depicts a period of greater erosion under a less developed catchment vegetation cover. Between 10.9 and 4.6 cal ka BP, the lake became a wetland characterised by shallow water with a reduced drainage network under warmer climate and/or reduced rainfall. From 4.6 cal ka BP, a second lacustrine phase developed driven by enhanced stream flow and sediment input subsequently accelerated by land use change. On a millennial scale, the two significant changes in the lake-catchment system and erosion regime at 10.9 and 4.6 cal ka BP may reflect a response to fluctuations in large-scale atmospheric circulation patterns. The eight short-term erosional events identified at 10.6, 7.8 cal ka BP, between 4.4–4.1, 3.5, 3.0–2.5, 1.9, 1.5, 1.1–0.8 cal ka BP, overlap well-known climate events. However, from 4.6 cal ka BP the climate-landscape relationship is amplified by rising anthropogenic impacts. Our data provide critical information on the paleoenvironmental evolution of CE Europe’s lowlands and facilitate discussion of the effects of millennial and centennial climatic shifts as expressed in the local environment.

Contemporary Controls on Terrestrial Carbon Characteristics in Temperate and Sub‐Tropical Australian Wetlands

AbstractA thorough understanding of controls over terrestrial sedimentary organic carbon characteristics in both the present and the past is pivotal to better understand atmospheric CO2 pathways into depositional sinks such as peats, swamps, and lakes. We explored the relationship between wetland sediment organic matter storage, climate (precipitation, temperature) and catchment vegetation data (catchment vegetation cover in percent; leaf carbon content in g/m2) by means of multivariate statistical analyses to investigate patterns of carbon deposition in modern wetlands and to provide a more robust framework for interpreting sediment bulk organic geochemistry as a proxy for past carbon cycling. Carbon and nitrogen elemental concentration and stable isotope composition were analyzed from sub‐surface sediments at 18 wetlands in eastern Australia. The statistical analyses indicate that variability in geochemical organic matter data in wetland sediments is best explained by geographic differences in catchment vegetation cover and, by inference, the balance of terrestrial versus aquatic organic matter input to the sediment. TOC/TN of aquatic matter may be additionally driven toward higher (terrestrial) values by nitrogen limitation in the catchment and the lakes. These processes explain up to ∼40% of the total variance in the sediment geochemistry (redundancy analyses). Up to ∼10% of the total variance may be attributed to post‐depositional processes and organic matter remineralization. The remaining ∼50% of total variance in the data may be attributed to local conditions across the sites, geochemical processes that were not captured in this study, or to the different timescales covered by the sediments at each site.

Catchment vegetation and erosion controlled soil carbon cycling in south-eastern Australia during the last two glacial-interglacial cycles

Vegetation structure in vast semi-arid to temperate continental land masses, such as Australia, plays a considerable role in global terrestrial carbon sequestration. However, whether soil carbon from these regions is a net atmospheric carbon source or sink remains contentious, introducing large uncertainties on long-term storage of vegetation-sequestered carbon dioxide. We investigate the interplay between catchment erosion quantified using uranium isotopes, vegetation (pollen), catchment carbon cycling, wetland response (diatoms), and lake carbon accumulation on glacial-interglacial timescales in south-eastern Australia. The analyses are applied to sediments from Lake Couridjah, in the Sydney Basin during the last (133.5 ka to 107.6 ka) and current (17.8 cal ka BP to present day) glacial-interglacial transitions. Robust phase-relationships between catchment erosion, vegetation composition and carbon cycling during both glacial-interglacial periods were revealed by statistical analyses. Vegetation structure had a direct control on catchment erosion, and, thus, on soil organic carbon (SOC) erosion in the catchment. Overall wetter and warmer peak interglacial conditions promoted the expansion of a canopy and mid-storey vegetation cover reducing catchment erosion, while simultaneously increasing SOC storage, catchment and lake primary productivity, and lake carbon storage. The results suggest increased terrestrial carbon sequestration in temperate Australian landscapes in warmer and wetter climates. • Novel trace metal isotope method quantifies “palaeo-sediment residence times” as proxy for catchment erosion • First continuous catchment erosion record for the last and current glacial-interglacial cycle in SE Australia • Link between catchment vegetation cover and erosion highlights the role of Australia as global carbon sink

Observations of water transparency in China’s lakes from space

Water transparency, usually denoted by Secchi disk depth (SSD), represents the first-order description of water quality and has important implications for the diversity and productivity of aquatic life. In China, lakes supply freshwater and ecosystem services to nearly a billion people. Therefore, real time monitoring of lake transparency is of great significance. Moreover, understanding how and why transparency varies in space and time in response to different driving forces is needed to understand, manage, and predict lake water quality. Based on the time-saving and low-cost Google Earth Engine cloud platform, this study developed a new algorithm for quickly mapping SDDs in Chinese lakes. SDDs were retrieved for 412 Chinese lakes (> 20 km2) for the period 2000–2018. Results demonstrated that lake water depth spatially differentiated transparency. Deep lakes usually had high transparency and water depth explained 88.81 % of the spatial variations. With increasing catchment vegetation coverage and lake water depth, 70.15 % of lakes witnessed increasing transparency during 2000–2018. Of these 42.72 % were significant (p < 0.05). Transparency of deep lakes was generally determined by phytoplankton density not sediment resuspension. Minimum transparency occurred in summer. Future increases in lake water levels in response to factors such as climate change may contribute to further improvements in transparency. Management should focus on controlling eutrophication and increasing vegetation cover in catchments.

Анализ динамики антропогенных изменений экосистем водосбора р. Кемь (бассейн Белого моря) с использованием данных Global Forest Change

The analysis of changes in the catchment vegetation cover as a result of industrial development of its territory, primarily deforestation, was carried out. For processing Landsat images, the spectral space modeling method was used, which provides higher reliability of the classification results compared to traditional methods. The most significant changes in the catchment occurred from the 1930s (the beginning of large-scale logging), until the end of the 1990s. Significantly, by more than 60 %, the area of old-growth forests decreased, their large fragments remained only in nature protected areas, as well as around large lakes and along large rivers, due to the presence of water protection zones. In the period from 2000 to 2018 due to deforestation, the area of productive forests decreased even more. Nevertheless, by 2019 the occurrence of secondary reforestation on significant areas (up to 70 %) is noted, which indicates a sufficiently high regeneration potential of the catchment ecosystems. To restore the spatial structure of the forest cover in the period before the start of the Landsat 5 operation, the method of tracking the trajectories of reforestation successions in the spectral space was used. A comparison with the results of the Global Forest Change 2000—2018 data (loss/gain) showed almost complete coincidence in cuttings (loss), but the method of reforestation trajectories showed many times higher results in forest gain, since it reveals forest regeneration at a much earlier stage. The developed methodology will be applied on the catchments of other tributaries of the White Sea, and the results will be used as input to an environmental-socio-economic cognitive model that predicts the state of ecosystems under climate changes and economic priorities.

Functional biogeography: Stoichiometry and thresholds for interpreting nutrient limitation in aquatic plants

Atmospheric N pollution may shift nutrient limitations in aquatic autotrophs from N to P or cause an intensification of P limitation in formerly pristine areas. Small changes in nutrient supply in oligotrophic lakes and rivers could lead to large changes in relative plant growth and yield with possible knock on effects on ecosystem carbon cycling through changes in the decomposition rate of their tissue. Previous biogeographical studies have shown inconsistent responses of plant nutrient tissue content and stoichiometry (functional traits) to external nutrient availability. Here we used a single species, Juncus bulbosus, to test the interplay between plant tissue nutrient (content and stoichiometry) and external environmental factors (local and catchment scale). We developed a comparative approach applicable globally to assess the thresholds for nutrient limitation in aquatic plants in the wild. Phosphorus in Juncus bulbosus tissue was negatively related to sediment organic matter (Fe root plaque limiting P uptake) and catchment vegetation cover (less P leaching to lakes). Our comparative approach revealed that the lack of increase in N plant tissue along the strong gradient in external N concentration may be explained by P limitation and strict plant tissue N:P ratio. Our comparative approach further showed that the nutrient content and stoichiometry of Juncus bulbosus was similar to other submerged aquatic plants growing in nutrient poor aquatic ecosystems. In southern Norway, mass development of Juncus bulbosus may be primarily triggered by changes in P availability, rather than CO2 or inorganic N, as previously thought, although co-limitations are also possible. If so, the mass development of Juncus bulbosus in oligotrophic aquatic ecosystems could be an early indicator of increasing P fluxes through these ecosystems which are less limited by N due to high atmospheric N deposition.

Nonstationarity driven by multidecadal change in catchment groundwater storage: A test of modifications to a common rainfall–run‐off model

AbstractMany parts of the world are experiencing a drying climatic trend with significant implications for water resources, especially where there is interaction between surface water and groundwater. Where drying leads to a shift in a catchment's hydrological regime, hydrological models may display bias in predictions and therefore degradation in their predictive capacity. We present two modifications to GR4J, a commonly used rainfall–run‐off model, that (a) allow the sensitivity of storage dependant evaporation and streamflow production to differ significantly, effectively mimicking “catchment memory” and (b) account for temporal variation in catchment vegetation cover, for example, due to land use change. We test the original and two modified models on a forested headwater catchment in the south‐west of Australia. In this catchment, a data set of more than 21,000 individual groundwater records collected over a period of more than 40 years chronicles a significant decline in catchment groundwater storage, resulting in a nonstationary streamflow regime. These longer‐term changes were overlaid with a shorter‐term hydrological response to clearing for bauxite mining and subsequent revegetation. The model structural modifications led to substantially improved streamflow prediction when compared with the original model, related to improved ability in the revised models' production store to match changes in the observed groundwater storage within the catchment. The performance of all three models and hence the apparent effectiveness of the modified models was dependent on the hydrological conditions in the calibration period. Best model fits were obtained when the calibration period encompassed both wetter and drier conditions in the hydrological record. The modified models presented here may reduce prediction bias for catchments in other parts of the world where long‐term shifts in hydrologic regime are being experienced and improve prediction for catchments with significant changes in vegetation cover.

A 7000-year environmental history and soil erosion record inferred from the deep sediments of Lake Pavin (Massif Central, France)

A 14-m long sedimentary sequence (core PAV12) was collected in the deepest part of Lake Pavin, a maar lake located in the French Massif Central. The PAV12 sedimentary sequence documents the lake's environmental evolution since its formation 7000 years ago. The relationships between the catchment's vegetation cover, erosion processes and changes in trophic status were shown using a multi-proxy characterization of mineral and organic fractions supported by palynological data. The record shows a succession of lithological units starting at the base with volcanoclastic material corresponding to the early stage of Lake Pavin. The deposition of organic-rich and diatomaceous sedimentary units above volcanoclastic material indicates an evolution toward a pristine lacustrine state. The Late Holocene environmental history of this lake is marked by two tipping points reflecting major environmental disturbances at ca. 4000 cal BP and after the deposition of erosive mass-wasting deposits (MWDs) at 1350 cal BP (AD 600) and 650 cal BP (AD 1300). The upper unit of core PAV12, which corresponds to the past 700 years, indicates that one of these MWDs was likely the driving force behind a major limnological change marked by a shift in redox-sensitive elements (i.e., current meromictic lacustrine state). The palynological diagram indicates a forested catchment where woodland clearances and agro-pastoral activities have remained limited except over the last 700 years. These findings suggest restricted human impact within the watershed compared to other regional archives. The reconstruction of the Lake Pavin erosion record determined from titanium and red amorphous particle fluxes highlights phases of enhanced erosion at ca. 6.5–5.5, 4.1–3.8, 3.5, 2.8–2.6, 1.6–1.4 cal kyr BP and during the Little Ice Age (LIA). A comparison between this erosion record, palaeoenvironmental archives from Western Europe and palaeoclimatic data supports an Atlantic signal driving precipitation patterns over Lake Pavin at centennial to millennial timescales. The influence of local human activities, even on a small scale, cannot be completely discounted as their impact on erosional processes may be amplified in a steep catchment such as that found in Lake Pavin.

Biophysical controls over concentration and depth distribution of soil organic carbon and nitrogen in desert playas

AbstractPlaya wetlands are important areas of soil organic carbon and nutrient storage in drylands. We conducted this study to assess how catchment biophysical variables control soil organic carbon and nitrogen in playas and how playas function differently than upland ecosystems. We found that playa organic carbon and nitrogen corresponded primarily with catchment vegetation cover and secondarily with catchment area, slope, and soil texture. The effect of increased organic matter production associated with high catchment vegetation cover overshadowed the potential effect of reduced run‐on. We also found soil carbon and nitrogen profiles to be significantly shallower in playas than uplands. This trend is correlated with evidence of sedimentation and shallow‐rooted plants in playas. Upland soils had a deeper carbon and nitrogen profile, which correlated with organic matter being generated by deeply rooted vegetation. In playas, C:N ratios remained constant through depth but in uplands, C:N ratios increased through depth. We found evidence that differences in rooting depth distributions and soil texture may explain these C:N variations between uplands and playas. In uplands, clay concentration increased with depth, whereas in playas, clay concentration did not change with depth, which highlighted the important role of sedimentation in these ecosystems. Our results suggest that small changes in playa catchment vegetation cover in response to climate change or grazing intensity would greatly impact playa soil organic carbon and nitrogen stocks. This effect would be due to the playa soils dependence on allochthonous organic matter and the large upland area that drains into playas.

From greening to browning: Catchment vegetation development and reduced S-deposition promote organic carbon load on decadal time scales in Nordic lakes.

Increased concentrations of dissolved organic carbon (DOC), often labelled “browning”, is a current trend in northern, particularly boreal, freshwaters. The browning has been attributed to the recent reduction in sulphate (S) deposition during the last 2 to 3 decades. Over the last century, climate and land use change have also caused an increasing trend in vegetation cover (“greening”), and this terrestrially fixed carbon represents another potential source for export of organic carbon to lakes and rivers. The impact of this greening on the observed browning of lakes and rivers on decadal time scales remains poorly investigated, however. Here, we explore time-series both on water chemistry and catchment vegetation cover (using NDVI as proxy) from 70 Norwegian lakes and catchments over a 30-year period. We show that the increase in terrestrial vegetation as well as temperature and runoff significantly adds to the reduced SO4-deposition as a driver of freshwater DOC concentration. Over extended periods (centuries), climate mediated changes in vegetation cover may cause major browning of northern surface waters, with severe impact on ecosystem productivity and functioning.

A model of the 4000-year paleohydrology (δ18O) record from Lake Salpetén, Guatemala

A simple mass-balance model provides insights into the influence of catchment vegetation changes and climate variability on the hydrologic and stable oxygen isotope (δ18O) evolution of Lake Salpetén, in the Maya Lowlands of northern Guatemala. Model simulations for the last 4000years incorporate pollen-inferred changes in vegetation cover and account for 75% of the variance observed in the biogenic carbonate δ18O record from a long lake sediment core. Vegetation-driven hydrologic changes, however, failed to capture the full range of late Holocene sediment core δ18O variability. The model requires incorporation of additional shifts in catchment vegetation cover, inclusion of regional precipitation changes, or likely both, to explain the fluctuations observed in the lake core oxygen isotope record. Climatic interpretation of the model results suggests that there was relatively greater moisture availability between about 2400 and 1800years ago, but increased δ18O values centered at ~3300, 2900, 500, and 200 calendar years before present (calyr BP) indicate abrupt precipitation decreases. There is evidence for protracted aridity between 1500 and 800calyrBP.

Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

Summary Quantitative tools to describe biological communities are important for conservation and ecological management. The analysis of trophic structure can be used to quantitatively describe communities. Stable isotope analysis is useful to describe trophic organization, but statistical models that allow the identification of general patterns and comparisons between systems/sampling periods have only recently been developed. Here, stable isotope‐based Bayesian community‐wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover (C3/C4): the Zambezi in Mozambique, the Tana in Kenya and the Rianila, the Betsiboka and Pangalanes Canal (sampled at Ambila) in Madagascar. Primary producers, invertebrates and fish of different trophic ecologies were sampled at each estuary before and after the 2010–2011 wet season. Trophic length, estimated based on δ15N, varied between 3·6 (Ambila) and 4·7 levels (Zambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at Ambila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the Betsiboka and Tana (C4‐dominated) had lower trophic diversity than the Zambezi and Rianila (C3‐dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources. There was seasonality in trophic structure at Ambila and Betsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For Ambila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the Betsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season. The comparative analysis of community‐wide metrics was useful to detect patterns in trophic structure and identify differences/similarities in trophic organization related to environmental conditions. However, more widespread application of these approaches across different faunal communities in contrasting ecosystems is required to allow identification of robust large‐scale patterns in trophic structure. The approach used here may also find application in comparing food web organization before and after impacts or monitoring ecological recovery after rehabilitation.

Quantifying total suspended sediment export from the Burdekin River catchment using the loads regression estimator tool

The loads regression estimator (LRE) was introduced by Wang et al. (2011) as an improved approach for quantifying the export of loads and the corresponding uncertainty from river systems, where data are limited. We extend this methodology and show how LRE can be used to analyze a 24 year record of total suspended sediment concentrations for the Burdekin River. For large catchments with highly variable discharge such as that of the Burdekin River, it is important to quantify loads and their uncertainties accurately to determine the current load and to monitor the effect of changes in catchment management. The extended methodology incorporates (1) multiple discounted flow terms to represent the effect of flow history on concentration, (2) a term that captures sediment trapping and spatial sources of flow in terms of the ratio of flow from above the Burdekin Falls Dam, and (3) catchment vegetation cover. Furthermore, we validated model structure and performance in relation to the application tested. We also considered errors in gauged flow rates of 10% that were consistent with the literature. The results for the Burdekin site indicate substantial variability in loads across years. The inclusion of vegetation cover as a predictor had a significant impact on total suspended sediment (TSS) concentration, with values up to 2.1% lower noted per increasing percentage of vegetation cover. TSS concentration was up to 38% lower in years with greater proportions of flow from above the dam. The extended LRE methodology resulted in improved model performance. The results suggest that management of vegetation cover in dry years can reduce TSS loads from the Burdekin catchment, and this is the focus of future work.

Characterising vegetation cover in relation to land use in the Inkomati catchment, South Africa, using Landsat imagery

Vegetation cover in catchments in semi-arid environments with distinct rain seasons is important in influencing water quality and availability through its effect on runoff and groundwater recharge. This study assessed catchment-scale vegetation cover and condition, indicated by land degradation and vegetation vigour, using recent rain season Landsat TM/ETM+ images supplemented by dry season images for comparison. Image classification into vegetation density categories was used in mapping land degradation, the bare land category used as indicator. Vegetation vigour indicates vegetation productivity levels, and has been shown to correlate with the NDVI in similar previous studies. The 30 savanna biome vegetation types in the catchment were used as strata for assessing relative vigour using NDVI values. The NDVI frequency distributions per vegetation stratum were normal (Gaussian), the location of whose peaks enabled comparisons. Land degradation could be mapped with certainty mainly in the vicinity of settlements. Rivers draining through degraded areas had elevated colour and turbidity values. As the NDVI profiles per vegetation type could be explained by the land use and landscape position context of the vegetation types, NDVI profiling proved useful for assessing vegetation condition. NDVI profiling of vegetation types is potentially useful in monitoring savanna vegetation condition using remotely sensed images.

Measuring stream macroinvertebrate responses to gradients of vegetation cover: when is enough enough?

Summary1. Management of stream biodiversity is often tightly linked with the restoration and protection of riparian and catchment vegetation. Despite that, there are no established guidelines on how much forest should be retained or replanted in riparian zones and surrounding catchments to maintain or re‐establish instream ecological integrity. In this study, we assess relationships between vegetation cover at multiple spatial scales (reach, segment and catchment) and macroinvertebrate metrics that reflect community structure, ecological condition and biodiversity at 138 Waikato, New Zealand, stream sites sampled in 2006.2. Percentage of catchment vegetation in native forest had stronger relationships with measured diversity and condition metrics than segment or reach scale measures of riparian vegetation. Functional feeding group metrics were weakly associated with upstream catchment vegetation cover.3. Of the macroinvertebrate metrics tested, the RIVPAC O/E and an organic pollution tolerance metric based on species presence–absence (Macroinvertebrate Community Index; MCI) had the strongest relationships with percentage native riparian vegetation, followed by the quantitative MCI and measures of the richness and relative abundance of Ephemeroptera, Plecoptera and Trichoptera faunas. The O/E and MCI indicated that catchments with 80–90% in native forest or scrub (low‐growing trees) were associated with faunas indicative of “clean” water quality.4. Of the biodiversity indices considered Fisher’s α Index of species richness had the strongest relationship with percent native riparian vegetation in the upstream catchment. There are no established thresholds for measuring biodiversity loss in New Zealand streams, but this analysis indicates that on average streams draining catchments with 40–60% upstream native vegetation cover retain 80% of the mean biodiversity present in pristine forest streams.5. This research indicates that riparian management aimed at enhancing macroinvertebrate biodiversity and the ecological condition of streams is likely to be more successful when focused on protecting and/or restoring headwater catchments rather than short stretches of stream.

Late Quaternary river terrace development in the Macgillycuddy's Reeks, southwest Ireland

Geomorphological, sedimentological, pedostratigraphical and palaeoecological analyses of fluvial and glacigenic deposits infilling the Gaddagh valley, Macgillycuddy's Reeks, southwest Ireland, are used to elucidate the patterns and controls of Late Quaternary valley floor development in a 3 km reach of the catchment lying immediately downvalley of two mid-basin lakes, Lough Gouragh and Lough Callee. A total of four Holocene alluvial terraces (Terrace Level, TL 2–5) and a modern floodplain (TL 6) have been identified and lie inset within a strath terrace comprising Late Quaternary (Midlandian) till (TL 1). The combination of mid-basin lakes and flanking strath terraces acted to decouple the Gaddagh channel from upper catchment and valley-side debris sources shortly after regional deglaciation. Postglacial fluvial terrace development in the study reach has therefore occurred primarily in response to hydrological changes and reworking of local valley floor deposits rather than catchment-wide debris supply changes. Pollen analyses of valley floor peat deposits interbedded with minerogenic alluvium indicate that anthropogenic disturbance of catchment tree cover had commenced by c.a 1690–1450 cal BC and that the catchment was largely cleared of woodland by later prehistoric times. Major phases of incision and alluviation represented by terraces TL 3–5, however, have been radiocarbon dated to the period after 250–530 cal AD and broadly correspond with Holocene fluvial records elsewhere in the region, upland Britain and northwest Europe. Although fluvial system responses to hydrological changes will have been promoted by anthropogenic disturbances of catchment vegetation cover, the timing of late Holocene incision and alluviation episodes are interpreted as reflecting enhanced flood frequencies and (or) magnitudes associated with late Holocene climatic shifts. In the Gaddagh Valley, however, we hypothesise that the headwater lakes Lough Gouragh and Lough Callee may also have exerted a critical control on the postglacial evolution of the valley floor. In particular, high-magnitude flooding is likely to have been instrumental in valley floor entrenchment and formation of TL 3, TL 4 and TL 5 terraces.