Pasture Catchment Research Articles

THE LINKS BETWEEN LAND USE AND WATER QUALITY FOR FRESHWATER PEARL MUSSEL, MARGARITIFERA MARGARITIFERA, IN THE RIVER SOUTH ESK, SCOTLAND

The freshwater pearl mussel, Margaritifera margaritifera, is an endangered species and its population has decreased rapidly over the last century. Scotland is the home to half of the known populations of M. margaritifera. Land use is a significant factor affecting water quality as well as the distribution of freshwater pearl mussels. Thirty eight sites in River South Esk were selected to investigate the impacts of land use on water conductivity, pH and the concentration of nitrate and phosphorus on the distribution of mussels. M. margaritifera was more abundant in habitats in woodland with low and stable water nutrient level. Water chemical analysis indicates that pollutant concentration is related to the vegetation of river catchments. River water passing woodland has a relatively better quality and overhanging boughs of trees create shadows which attract mussels. Livestock pasture catchments seem to have less significant chemical effects, but animal activities may disturb the habitat of mussels and increase water turbidity. Water pollution in irrigated crop land is relatively higher. Heather moorland is of less concern because of its inappropriate channel type for mussels. Waters in the vicinity of housing, roads and bridges seem to be avoided by mussels. Margaritifera margaritifera did not show any preference on the type of shadows. Living mussels have been discovered at the sites which have shadows created by overhanging branches or high riverbanks.

Quantifying sources of suspended sediment in three size fractions

Identifying of the sources, stores and pathways of sediments in a catchment is essential to accurately target management actions designed to reduce sediment delivery to receiving waters. Fingerprinting the source of sediment using geochemical properties has increasingly been accepted as an accurate approach for quantifying the contribution of different sources to river sediment discharge. In this study, we seek to examine the effect of particle size and location of the sources on their contribution to suspended sediments. Geochemical tracers (n = 41) were employed to calculate proportional contributions of sediment to Emu Creek, a predominantly pastoral catchment (911 km2) in south-eastern Queensland, Australia. The study focused on two high flow events (10- and 6-year return periods) and some lower flow events which occurred during the 18 months from October 2011 to March 2013. Source contributions were determined at eight spatially distributed sites in major tributaries and along the main channel of Emu Creek. Source determination at the in-stream sites was done using end member samples (based on the underlying rock type) collected upstream of the site of interest, thus indicating how different sources dominate at different locations downstream. To examine whether different size fractions shared similar provenances, three size fractions of both source and suspended samples including fine silt and clay (<10 μm), silt (10–63 μm) and fine sand (63–212 μm) were analysed. The source apportionment results using the distribution mixing model indicate that particle size and location of sources within a catchment are major factors that affect the measured contribution of sources to suspended sediments. The closer a suspended sediment sampling site is to a potential source, the more likely it is that source of sediment will dominate the material being sampled. For all size fractions, proximal sources of sediment make a higher contribution to suspended sediments than distal sources. This indicates that management actions should be focused on the more proximal sources to the point of interest/impact. Although proximal soil sources were major contributor of sediments in all three size fractions, the percentage of contribution greatly vary in different size fractions, emphasising the need to trace the size fraction which is causing the downstream problems.

Catchment‐scale Richards equation‐based modeling of evapotranspiration via boundary condition switching and root water uptake schemes

AbstractIn arid and semiarid climate catchments, where annual evapotranspiration (ET) and rainfall are typically comparable, modeling ET is important for proper assessment of water availability and sustainable land use management. The aim of the present study is to assess different parsimonious schemes for representing ET in a process‐based model of coupled surface and subsurface flow. A simplified method for computing ET based on a switching procedure for the boundary conditions of the Richards equation at the soil surface is compared to a sink term approach that includes root water uptake, root distribution, root water compensation, and water and oxygen stress. The study site for the analysis is a small pasture catchment in southeastern Australia. A comprehensive sensitivity analysis carried out on the parameters of the sink term shows that the maximum root depth is the dominant control on catchment‐scale ET and streamflow. Comparison with the boundary condition switching method demonstrates that this simpler scheme (only one parameter) can successfully reproduce ET when the vegetation root depth is shallow (not exceeding approximately 50 cm). For deeper rooting systems, the switching scheme fails to match the ET fluxes and is affected by numerical artifacts, generating physically unrealistic soil moisture dynamics. It is further shown that when transpiration is the dominant contribution to ET, the inclusion of oxygen stress and root water compensation in the model can have a considerable effect on the estimation of both ET and streamflow; this is mostly due to the water fluxes associated with the riparian zone.

Chemical properties of soil and runoff water under different land uses in Abbottabad, Pakistan

This study examined properties of soil and runoff water under different land uses: forestry, pasture, cropping and fallow. The moisture level was found higher in the forest soil, while fallow and pasture soils showed a similar level of moisture. In top soil, the water holding capacity of pasture and forest soils was higher than other soils, especially that under cropping; the sub-soil held more water (12.1 %) than the top soil (10.3 %). The lower moisture level in cultivated or fallow lands could be attributed to the lower soil organic matter. Carbon concentration in the soils varied in the order forest > pasture > fallow > crop land. Across land uses, the concentrations of cations differed in the order: Ca > Mg > Na > K. Relatively higher concentrations of nutrients and lower pH were obtained in the top soil and sub-soil of the forest land. Forest and pasture catchments showed lower Na in soil. Regression analysis showed higher correlation between soil carbon and soil moisture, water holding capacity and nutrients. The nutrients concentrations were higher in forest soil and lowest in the soils of fallow and agricultural lands. The cations in the runoff water varied in the order Ca > Mg > Na > K, being highly consistent with that in the soil in each land use. Calcium concentrations in the runoff varied in the order forest > pasture > crop > fallow. Magnesium concentration was higher in forest runoff than other land uses, whereas higher K concentration was in pasture runoff. Higher total solids in the runoff of fallow land indicate soil erosion. The study highlights the value of plantation as a measure for land management.

Hydrologic tracers and thresholds: A comparison of geochemical techniques for event-based stream hydrograph separation and flowpath interpretation across multiple land covers in the Panama Canal Watershed

Stream hydrograph separation using naturally occurring geochemical tracers holds great potential for elucidating mineral weathering and solute transport. This study addresses a critical need to characterize catchment runoff generation in the humid tropics using multiple natural tracers for hydrograph separation and concentration/discharge (C/Q) hysteresis analysis. We use hydrometric and geochemical data collected at the start of the wet season from three small, steep catchments located in the humid seasonal tropics of central Panama that differ primarily in land cover. We apply a dual source hydrograph separation model between two end-members: new event water precipitation and pre-event water stored in the catchment. We compare the effectiveness of electrical conductivity (EC) and stable water isotopes (δD and δ18O) tracers for identifying precipitation event water in stream runoff using across forested (1.43km2), mixed land use ‘mosaic’ (1.82km2) and pasture (0.42km2) catchments. Hysteretic C/Q loops are analyzed for flowpath interpretation using δD, Ca2+, Mg2+, Na+, K+, Cl−, and SO42−. During a medium-large magnitude event on May 23, 2013, forest and mosaic stream δD, Ca2+, Mg2+, and Na+ exhibited clockwise hysteresis, SO42− exhibited anticlockwise hysteresis, and K+ and Cl− each showed no hysteresis. EC as a surrogate for total dissolved solids agrees acceptably with stable water isotope hydrograph separations during small peak runoff events (<3mm/h). However, isotope and conductivity tracers strongly disagree during a large runoff event (>10mm/h) in the mosaic catchment. Early wet-season events indicate lower event water fractions than events farther into the wet season. Despite previous work showing land cover strongly controls storm runoff efficiencies, hydrograph separation and hysteresis analyses only indicate weak event water delivery differences between the paired forest and mosaic catchments.

Nitrogen Dynamics in Hydrological Flow Paths of a Small Tropical Pasture Catchment

In this paper we report nitrogen (N) dynamics within hydrological flow paths of a small tropical pasture catchment within the Atlantic Rainforest region in Natividade da Serra, São Paulo State, Brazil. By collecting soil solution through 27 tension lysimeters, surface runoff through 9 plots, groundwater through one well and one stream over the course of a year, N species concentration and fluxes could be clarified. All hydrological flow paths were dominated by organic N (~60–85%). This finding is explained as a consequence of a drop of soil N cycling rates and N gaseous fluxes previously reported in the literature. Nitrogen input via bulk precipitation (~3.5kgNha−1year−1) exceeded N hydrological output through stream water (~2kgNha−1year−1). Similar findings have been described for pastures of the Brazilian Amazon Basin. If pastures like these are maintained without fertilization, catchments whose land use is old pastures may not be an important direct source of inorganic N for downstream regions.

A comparison of streamflow, salt and water balances in adjacent farmland and forest catchments in south‐western Victoria, Australia

AbstractA study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south‐western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20‐month study period. Monthly streamflow was always greater in the pasture‐dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture‐based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954–2012) summer rainfall. Streamflow peaks in the plantation‐based catchment were smaller than in the pasture‐dominated system. Flow duration curves show differences between the pasture and plantation‐dominated catchments and affect both high‐flow and low‐flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south‐eastern Australia, but this benefit is offset by reduced total streamflow. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Characterizing rainfall-runoff signatures from micro-catchments with contrasting land cover characteristics in southern Amazonia

On the basis of interactions between landscape characteristics and precipitation inputs, watersheds respond differently to different climatic inputs. The objective of this study was to quantitatively characterize controls on runoff generation from two first order micro-catchments in the Amazonia region. The study investigated the variation of hydrological signatures at micro-catchment scale and related these to landscape and land cover differences and weather descriptors that control the observed responses. One catchment is a pasture cleared of all natural vegetation in the early 1980s, and the second catchment is a primary tropical forest with minor signs of disturbance. Water levels and meteorological variables were continuously monitored during the study period (December 2012–May 2013). Water level measurements were converted to discharge, evapotranspiration was quantified using Penman–Monteith equation and catchment pedohydrological properties were also determined. During the study period, mean total rainfall was 1200 mm, and direct runoff ratios were 0.29 and 0.12 for the pasture and forest catchments, respectively. Base flow index was relatively high in the forest catchment (0.76) compared with pasture catchment (0.63). Results from this study showed that the pasture catchment had a 35% higher mean stream flow. Analysis of selected individual rainstorm events also showed peak discharges, which were attained much faster in the pasture catchment compared with the forest catchment. At both sites, rainfall-runoff responses were highly dependent on surface and subsurface flow generation. Overland flow was observed in the pasture site during intense rainfall events. The pasture catchment exhibited higher event water contribution than the forest catchment. Findings from this research suggest that shallow lateral pathways play a significant role in controlling runoff generation processes in the forest catchment, whereas infiltration excess runoff generation processes dominate in the pasture catchment. The findings in this study suggest that the conversion of forest to pasture may lead to important changes in runoff generation processes and water storage in these head water catchments. Copyright © 2014 John Wiley & Sons, Ltd.

Spatial structure of surface soil water content in a natural forested headwater catchment with a subtropical monsoon climate

Summary The surface or near-surface soil moisture at the interface between atmospheric and terrestrial environments has significant implications for the complex interactions between hydrological processes and ecosystems. Although a number of previous studies have reported the spatial patterns and structures of surface moisture in pasture environments based on large sample sizes, information regarding the detailed spatial patterns and structure of surface moisture in a natural forest environment is still sparse, particularly for steep headwater catchments due to the labor intensity involved and the difficulty of making field measurements. In this study, we measured the detailed surface soil water content at depths of 0–12 cm and 0–20 cm at 470 measurement points using the TDR (time domain reflectometry) method. Thirteen surveys were conducted within 1 year in a steep natural forested headwater catchment with a subtropical monsoon climate in Taiwan. The sample and model variograms were used to evaluate the spatial structure of the surface soil moisture. We also compared the spatial structures of surface moisture in this study with those in a similar study conducted in a flat pasture catchment ( Western et al., 1998 ). For the results at our site, exponential model variograms with the nugget effect well fitted sample variograms, indicating an obvious regional dependence of surface moisture and stationary spatial structures in all surveys. The geostatistical structural characteristics of the nugget varied between 22.70 and 47.40 (% V/V) 2 ; the sill varied between 54.99 and 98.51 (% V/V) 2 ; and the range varied between 10.20 and 58.65 m. The nugget, sill, and range all increased with an increase in soil moisture. The notable anisotropy under dry conditions was attributed to the year-round surface runoff pathway. The sample variograms that represented the spatial structure of soil moisture and reliably estimated the nugget, sill, and range required a sample size of at least 235 at our 0.15-ha site (i.e., a measurement resolution of at least 6.4 m 2 per sample). The pattern of soil moisture was relatively stationary in two gullies and on the side of a hillslope, but it varied on the valley-head hillslope depending on whether conditions were dry or wet. In contrast to previous results for a flat pasture catchment ( Western et al., 1998 ), our results produced a right-skewed histogram of soil moisture under dry or moderately wet conditions, variograms that tended to increase with an increase in soil moisture, anisotropy of soil moisture structure under dry, but not wet, conditions, a need for a 55 times higher measurement resolution associated with the large sample size, and a larger nugget effect in the steep natural forested headwater catchment. This study identified the spatial structure and patterns of surface soil moisture as the primary step in understanding hydrologic processes in a natural forested headwater catchment.

Effect of land cover and use on dry season river runoff, runoff efficiency, and peak storm runoff in the seasonal tropics of Central Panama

[1] A paired catchment methodology was used with more than 3 years of data to test whether forests increase base flow in the dry season, despite reduced annual runoff caused by evapotranspiration (the “sponge-effect hypothesis”), and whether forests reduce maximum runoff rates and totals during storms. The three study catchments were: a 142.3 ha old secondary forest, a 175.6 ha mosaic of mixed age forest, pasture, and subsistence agriculture, and a 35.9 ha actively grazed pasture subcatchment of the mosaic catchment. The two larger catchments are adjacent, with similar morphology, soils, underlying geology, and rainfall. Annual water balances, peak runoff rates, runoff efficiencies, and dry season recessions show significant differences. Dry season runoff from the forested catchment receded more slowly than from the mosaic and pasture catchments. The runoff rate from the forest catchment was 1–50% greater than that from the similarly sized mosaic catchment at the end of the dry season. This observation supports the sponge-effect hypothesis. The pasture and mosaic catchment median runoff efficiencies were 2.7 and 1.8 times that of the forest catchment, respectively, and increased with total storm rainfall. Peak runoff rates from the pasture and mosaic catchments were 1.7 and 1.4 times those of the forest catchment, respectively. The forest catchment produced 35% less total runoff and smaller peak runoff rates during the flood of record in the Panama Canal Watershed. Flood peak reduction and increased streamflows through dry periods are important benefits relevant to watershed management, payment for ecosystem services, water-quality management, reservoir sedimentation, and fresh water security in the Panama Canal watershed and similar tropical landscapes.

Agricultural Diffuse Nutrient Pollution Transport in a Mountain Wetland Complex

Wetlands in mountain environments provide critical ecosystem services but are increasingly threatened by agricultural land use intensification. This study evaluates agricultural nonpoint source nutrient pollution transport in a wetland–stream–lake complex in a mountain, tussock grassland catchment in the South Island, New Zealand. Flow and water-quality monitoring in the Lake Clearwater catchment during three flow events from May to August 2010 (autumn high flow, winter low flow, and winter high flow) showed high concentrations and exceedances of water quality guidelines for total nitrogen (TN) and total phosphorus (TP) in small ephemeral streams draining agricultural land during high flows. Concentrations were attenuated through the wetlands to below guidelines, with the exception of TN which still remained slightly higher. Most TN was in the organic form above and below the wetland, suggesting N sources from animal waste/agricultural land and organic material and vegetation within the wetland. Most TP was particulate associated with suspended solids during high flows. Dissolved forms of N and P generally were below guidelines. Flows and loads (instantaneous and daily) increased at the lake outlet during winter high flow, indicating unaccounted sources to the lake from groundwater, the wetlands, or the lake sediments, and seasonal N saturation. Infiltration losses to shallow groundwater along the main perennial tributary likely re-appear as discharge to the wetlands and lake downstream. Surface–groundwater interactions play a dominant role in N transport to the wetland complex due to highly permeable soils and glacial alluvial deposits. Loads and unit loads of TN and TP were also elevated in the ephemeral streams. Results show that TN and TP concentrations and unit loads during high flows in ephemeral streams in this mountain grassland catchment are similar to, or higher than, values for impacted lowland pasture catchments. Although impacts to the wetland ecosystem have not been observed to date, the lake is shifting toward a mesotrophic state, and further research is needed to elucidate impacts of nutrient loads and help meet conservation and restoration goals.

Drivers of Leaf Decomposition in Two Wetland Types in the Arkansas River Valley, U.S.A.

White Oak Bayou watershed in the Arkansas River Valley is losing wetlands rapidly that could alter regional carbon cycles. Leaf decomposition of ash and oak were used to assess carbon cycling in five flat and five backwater wetlands within forested (54 %), urban (30 %), and pasture (7 %) catchment. Wetlands were dry in summer and wet the remaining year. Backwaters were expected to have faster decomposition rates from longer wet periods and more nutrients that would increase microbial and macroinvertebrate consumption. Backwaters held more water than flats and decomposition of both tree species was faster in backwaters (k:0.0032 ± 0.0007 day−1) compared to flats (k:0.0026 ± 0.0008 d−1, p = 0.018). Ash (0.0035 ± 0.0006 day−1) decomposed faster than oak (0.0023 ± 0.0005 day−1, p < 0.0001). Variation in ash decomposition rates was explained by inundation time and ammonium concentration. Variation in oak decomposition rates was explained by surrounding forest and nitrite + nitrate concentrations. Minor variations in hydrology affected decomposition rates of fast-breakdown leaf species, while differences in surrounding land use and nutrient concentrations affected rates of slow-breakdown species. Environmental factors altered by changing land use have important consequences for leaf decomposition. This study helps us to understand the influence that anthropogenic changes have on wetland function as urbanization continues to encroach upon wetlands in Arkansas.

Consequências hidrológicas da mudança de uso da terra de floresta para pastagem na região da floresta tropical pluvial atlântica

The Atlantic rain forest is the most endangered ecosystem in Brazil. Its degradation has started since 1500 when the European settlers arrived. Despite of all land use changes that have occurred, hydrological studies carried out in this biome have been limited to hydrological functioning of rain forests only. In order to understand the hydrological consequences of land-use change from forest to pasture, we described the hydrological functioning of a pasture catchment that was previously covered by tropical rain forest. To reach this goal we measured the precipitation, soil matric potential, discharge, surface runoff and water table levels during one year. The results indicated that there is a decrease in surface soil saturated hydraulic conductivity. However, as low intensity rainfall prevails, the lower water conductivity does not necessarily leads to a substantially higher surface runoff generation. Regarding soil water matric potential, the pasture presented higher moisture levels than forest during the dry season. This increase in soil moisture implies in higher water table recharge that, in turn, explain the higher runoff ratio. This way, land-use change conversion from forest to pasture implies a higher annual streamflow in pasture catchments. Nonetheless, this increase in runoff due to forest conversion to pasture implies in losses of biological diversity as well as lower soil protection.

Conversion of the coastal Atlantic forest to pasture: Consequences for the nitrogen cycle and soil greenhouse gas emissions

We evaluated how land use change affected the nitrogen cycle and greenhouse gas fluxes. We measured soil temperature and water-filled pore space (WFPS), as well as nitrate and ammonium concentrations, mineralization and nitrification rates, and flux of CH 4, CO 2 and N 2O in soils of pasture catchment and in soils of a forest catchment located on the north coast of the State of São Paulo. The main vegetation type in the forest catchment is primary Atlantic Montane Forest, while the pasture is an unfertilized 40-year old area planted with Brachiaria humidicola. Four plots were used for monthly sampling in each land use for an entire year. Soil temperature was always higher in pasture than in forest soils, while WFPS was lower in the pasture in relation to forest soils. Pasture soils were a weak source of CH 4 during the winter months and a less strong sink of methane than the forest soils during the rainy summer months of the year. The annual median CH 4 uptake was −1.8 ± 1.0 mg m −2 d −1 in the forest in contrast to −0.6 ± 0.9 mg m −2 d −1 in pasture soils. CO 2 emissions were similar in the winter, but higher in the summer months in pasture soils in relation to forest soils. The annual median flux in the forest was 4.2 ± 1.5 μmol m −2 s −1 and increased in the pasture to 6.5 ± 2.9 μmol m −2 s −1. In contrast, N 2O fluxes were smaller in the pasture (0.3 ± 0.7 ng cm −2 h −1) than in forest soils (0.5 ± 0.5 ng cm −2 h −1).

Attenuation of Nitrogen, Phosphorus and E. coli Inputs from Pasture Runoff to Surface Waters by a Farm Wetland: the Importance of Wetland Shape and Residence Time

Water quantity and quality were monitored for 3 years in a 360-m-long wetland with riparian fences and plants in a pastoral dairy farming catchment. Concentrations of total nitrogen (TN), total phosphorus (TP) and Escherichia coli were 210–75,200 g N m−3, 12–58,200 g P m−3 and 2–20,000 most probable number (MPN)/100 ml, respectively. Average retentions (±standard error) for the wetland over 3 years were 5 ± 1%, 93 ± 13% and 65 ± 9% for TN, TP and E. coli, respectively. Retentions for nitrate–N, ammonium–N, filterable reactive P and particulate C were respectively −29 ± 5%, 32 ± 10%, −53 ± 24% and 96 ± 19%. Aerobic conditions within the wetland supported nitrification but not denitrification and it is likely that there was a high conversion rate from dissolved inputs of N and P in groundwater, to particulate N and P and refractory dissolved forms in the wetland. The wetland was notable for its capacity to promote the formation of particulate forms and retain them or to provide conditions suitable for retention (e.g. binding of phosphate to cations). Nitrogen retention was generally low because about 60% was in dissolved forms (DON and NOX–N) that were not readily trapped or removed. Specific yields for N, P and E. coli were c. 10–11 kg N ha−1 year−1, 0.2 kg P ha−1 year−1 and ≤109 MPN ha−1 year−1, respectively, and generally much less than ranges for typical dairy pasture catchments in New Zealand. Further mitigation of catchment runoff losses might be achieved if the upland wetland was coupled with a downslope wetland in which anoxic conditions would promote denitrification.

Biodiversity values of small headwater streams in contrasting land uses in the Auckland region

The biodiversity values of 12 small headwater streams (catchments mostly <30 ha) were evaluated. Densities of aquatic macroinvertebrates were the same or higher in three headwater habitats (flowing water, isolated pools and wet mud) as in adjacent perennial streams. Alpha (per sample) richness of all aquatic macroinvertebrates and of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa were as high in headwater flowing habitats and isolated pools as in perennial streams. Gamma (landscape-level) and beta (taxa turnover) richness appeared to be similar among isolated pools, mud habitats and perennial streams, but higher in headwater flowing habitats. Community composition was very similar among headwater flowing, isolated pool and perennial habitats. Some taxa in headwater habitats were headwater specialists, but none was identified as endemic to headwaters. Thus, macroinvertebrate evidence indicates that headwater streams should be given similar protection status to perennial reaches. Headwaters in pasture catchments had lower EPT richness than native forest headwaters. Riparian native woody vegetation appeared effective in maintaining EPT richness and community composition similar to the native forest condition.

Response of streamflow to afforestation and thinning at Red Hill, Murray Darling Basin, Australia

Competition for water resources in Australia’s Murray Darling Basin has resulted in plans to account for water used by various land use change activities including plantation forests. To date generalised forest conversion models have been used to assess the likely impacts of future afforestation. These models are a useful starting point but do not account for forest age or silvicultural intervention such as thinning. A twenty year record from the Red Hill paired catchment study was analysed to show that forest age is a significant factor in determining the streamflow response to afforestation. Compared to the Kileys Run pasture catchment, streamflow in the Red Hill catchment afforested with Pinus radiata plantations steadily declined, particularly after age 6 years when stand basal area rapidly increased. Mixed effect model analysis indicated that over the first 20 years of the rotation the mean annual impact of afforestation with pines was 155 mm. The modelled impact peaked at 211 mm in year 14 prior to thinning. Thinning at age 14 years had a significant positive effect on streamflow that has persisted for at least 6 years. Drought conditions coupled with a process of recharging the catchment soils contributed to a delayed response to thinning. Factors such as forest age and thinning should be incorporated into models used in water resources planning to more accurately predict the hydrological effects of afforestation.

A model framework to assess the effect of dairy farms and wild fowl on microbial water quality during base-flow conditions

There is concern regarding microbial water quality in many pastoral catchments in New Zealand which are home to numerous livestock and wild animals. Information on microbial impacts on water quality from these animals is scarce. A framework is needed to summarise our current knowledge and identify gaps at the scale of an individual farm. We applied a Monte Carlo modelling approach to a hypothetical dairy farm based on the extensive data sets available for the Toenepi Catchment, Waikato, New Zealand. The model focused on quantifiable direct inputs to the stream from ducks, cows and farm dairy effluent (FDE) during base-flow conditions. Most of the inputs of Escherichia coli from dairy farms occur sporadically and, therefore, have little effect on the expected median stream concentrations. These sporadic inputs do however, have a strong influence on extrema such as 95th percentile values. Current farm mitigations of fencing streams and using improved management practices for applying FDE to land, such as low application rate deferred FDE irrigation systems, would appreciably reduce faecal microbial inputs to the stream. However, the concentrations of E. coli in rural streams may not reduce as much as expected as wild fowl living in streams would have a larger effect on water quality than a farm in which environmental mitigations are widely implemented.

Differential behaviour of Escherichia coli and Campylobacter spp. in a stream draining dairy pasture

The faecal indicator bacterium Escherichia coli and thermotolerant Campylobacter spp., which are potentially pathogenic, were investigated in the Toenepi Stream draining a pastoral catchment dominated by dairying. Bacteria concentrations were monitored routinely at fortnightly intervals over 12 months and intensively during storm events to compare the transport dynamics of bacterial indicator and pathogen under varying hydro-meteorological conditions. Routine monitoring indicated median concentrations of 345 E. coli MPN 100 ml(-1) and relatively low concentrations of 2.3 Campylobacter MPN 100 ml(-1). The bacterial flux was three orders of magnitude greater under elevated stream flow compared with base-flow. E. coli peak concentrations occurred very close to the turbidity peak and consistently ahead of the Campylobacter spp. peak (which was close to the hydrograph peak). We postulate that, under flood conditions, the E. coli peak reflects the entrainment and mobilisation of in-stream stores on the flood wave front. In contrast, Campylobacter spp. are derived from wash-in from land stores upstream and have travelled at the mean water velocity which is slower than the speed of the flood wave. Our findings of different dynamics for E. coli and Campylobacter spp. suggest that mitigation to reduce faecal microbial impacts from farms will need to take account of these differences.

A GIS method for assessing the zone of human-environmental impact around archaeological sites: a test case from the Late Neolithic of Wadi Ziqlâb, Jordan

Assessing the impact of prehistoric sites on their local environment is difficult to accomplish with standard archaeological methods. Simulation modeling offers a solution to this issue, but it is first necessary to delimit a site catchment, or “zone of impact”, around archaeological sites in which to carry out human–environment interaction modeling. To that end, I have developed a new method for GIS-based catchment reconstruction and distilled it into a custom module ( r.catchment) for GRASS GIS, which calculates catchments of a given area based on anisotropic travel costs from a point of origin. One method of applying this new module in exploratory catchment modeling is discussed using the pastoral economy of the Late Neolithic period in Wadi Ziqlâb, Northern Jordan as a test case. A model of Late Neolithic herding economy and ecology is constructed, which combines data from archaeology, phytogeography, range science, agronomy, and ethnohistory. Four sizes of pastoral catchments are then derived using r.catchment, and the herd ecology model is used to estimate the stocking-rate (carrying capacity) of mixed goat and sheep herds for each catchment. The human populations these herd numbers could support (between 3 and 630 people in the Wadi) are then compared with human population estimates derived from household architectural analyses (between 18 and 54 people in the Wadi) to determine the most probable catchment configurations. The results indicate that the most probable zone of impact around the known Late Neolithic sites in Wadi Ziqlâb was somewhere between 9 and 20 square kilometers, delineated by 3 and 4.5 km pasture radii respectively.