Minimizing irrigation water demand: An evaluation of shifting planting dates in Sri Lanka

Climate change coupled with increasing demands for water necessitates an improved understanding of the water–food nexus at a scale local enough to inform farmer adaptations. Such assessments are particularly important for nations with significant small-scale farming and high spatial variability in climate, such as Sri Lanka. By comparing historical patterns of irrigation water requirements (IWRs) to rice planting records, we estimate that shifting rice planting dates to earlier in the season could yield water savings of up to 6%. Our findings demonstrate the potential of low-cost adaptation strategies to help meet crop production demands in water-scarce environments. This local-scale assessment of IWRs in Sri Lanka highlights the value of using historical data to inform agricultural management of water resources when high-skilled forecasts are not available. Given national policies prioritizing in-country production and farmers’ sensitivities to water stress, decision-makers should consider local degrees of climate variability in institutional design of irrigation management structures.     

Impact of conservation areas on trophic interactions between apex predators and herbivores on coral reefs

Apex predators are declining at alarming rates due to exploitation by humans, but we have yet to fully discern the impacts of apex predator loss on ecosystem function. In a management context, it is critically important to clarify the role apex predators play in structuring populations of lower trophic levels. Thus, we examined the top‐down influence of reef sharks (an apex predator on coral reefs) and mesopredators on large‐bodied herbivores. We measured the abundance, size structure, and biomass of apex predators, mesopredators, and herbivores across fished, no‐take, and no‐entry management zones in the Great Barrier Reef Marine Park, Australia. Shark abundance and mesopredator size and biomass were higher in no‐entry zones than in fished and no‐take zones, which indicates the viability of strictly enforced human exclusion areas as tools for the conservation of predator communities. Changes in predator populations due to protection in no‐entry zones did not have a discernible influence on the density, size, or biomass of different functional groups of herbivorous fishes. The lack of a relationship between predators and herbivores suggests that top‐down forces may not play a strong role in regulating large‐bodied herbivorous coral reef fish populations. Given this inconsistency with traditional ecological theories of trophic cascades, trophic structures on coral reefs may need to be reassessed to enable the establishment of appropriate and effective management regimes. El Impacto de las Áreas de Conservación sobre las Interacciones Tróficas entre los Depredadores Dominantes y los Herbívoros en los Arrecifes de Coral     

Biomasses,catch rates and abundances of demersal fishes,particularly predators of prawns,in a tropical bay in the Gulf of Carpentaria,Australia

The demersal fish fauna of Albatross Bay, in the eastern Gulf of Carpentaria, northern Australia, was sampled on seven cruises from August 1986 to November 1988, using a random stratified trawl survey. Four depth zones between 7 and 45 m were sampled during both day and night. The mean biomass of fish from all seven cruises was 297 kg ha^–1 for days trawls and 128 kg ha^–1 for night trawls. The overall mean catch rates were 922 kg h^–1 for day trawls and 412 kg h^–1 for night trawls. There were marked differences between cruises in both the biomass and catch rate. Approx 890 000 fish of 237 species were collected. Of these, 25 species comprised 82% of the total biomass and 74% of the overall catch rate. The dominant families were Leiognathidae, Haemulidae and Clupeidae, with Sciaenidae and Dasyatidae important at night.Leiognathus bindus was the most abundant species. Twenty-five species occurred in more than 50% of trawls, withCaranx bucculentus the most frequently caught (96% of all trawls). Thirty four species were predators on prawns; their absolute mean biomass was 50 kg ha^–1 during the day and 39 kg ha^–1 at night. The corresponding catch rates were 171 and 125 kg h^–1. Multiple-regression analyses were used to discriminate the effects of diel, seasonal, depth and cruise patterns. Of the 31 most abundant species, 15 showed diel patterns of abundance; 11 species showed seasonal patterns of abundance; 23 species had differential depth distribution; and 13 species showed significant cruise-to-cruise variation in abundance. Cruise variations in abundance were tested against salinity, temperature, tidal exchange, plankton biomass and prawn abundances as well as periods (and lags) of total rainfall prior to sampling. Only total rainfall showed any significant correlation. Total rainfall over a period of 6 wk immediately prior to sampling showed significant positive correlations with the abundances of five species, with overall daytime catch rates, and with the suite of 34 prawn predators. Rainfall and river runoff into Albatross Bay were significantly correlated. In Albatross Bay, the complex of factors affecting fish abundances and the magnitude of between-cruise differences indicate that such tropical communities may be unpredictable and are not seasonally constant. The high catch rates in Albatross Bay relative to similar tropical areas elsewhere are discussed and attributed to the light exploitation of the Albatross Bay stocks. Other than a prawn fishery, there is no commercial trawling in Albatross Bay. Hence, the only fishing mortality is a result of by-catch from prawn trawling. The annual total of such fish by-catch is probably less than 10% of the estimated standing stock of 93 000 tonnes.     

Duplicate sampling reproducibility of atmospheric residues of herbicides for paired pan and high-volume air samplers

The reproducibility of collection of atmospheric residues of the herbicides 2,4-D and triallate as bulk (wet plus dry) deposition samples by paired pan samplers and as particulate (filter) and vapour (PUF/XAD-2 resin cartridge) samples by paired high-volume air samplers was determined. Variability of herbicide concentrations in paired bulk deposition samples was within 25% for 65 and 80% of the samples for 2,4-D and triallate, respectively, with approximately 90% of the paired samples being within a factor of 2 for both herbicides. The vapour samples of 2,4-D and triallate showed similar reproducibilities. The highest reproducibility was observed for the filter samples with 92% of the paired data sets for 2,4-D being within 25% variability. No triallate was detected in the filter samples.     

Cover crop effects on nitrous oxide emission from a manure-treated Mollisol

Agriculture contributes 40–60% of the total annual N₂O emissions to the atmosphere. Development of management practices to reduce these emissions would have a significant impact on greenhouse gas levels. Non-leguminous cover crops are efficient scavengers of residual soil NO₃, thereby reducing leaching losses. However, the effect of a grass cover crop on N₂O emissions from soil receiving liquid swine manure has not been evaluated. This study investigated: (i) the temporal patterns of N₂O emissions following addition of swine manure slurry in a laboratory setting under fluctuating soil moisture regimes; (ii) assessed the potential of a rye (Secale cereale L.) cover crop to decrease N₂O emissions under these conditions; and (iii) quantified field N₂O emissions in response to either spring applied urea ammonium nitrate (UAN) or different rates of fall-applied liquid swine manure, in the presence or absence of a rye/oat winter cover crop. Laboratory experiments investigating cover crop effects N₂O emissions were performed in a controlled environment chamber programmed for a 14 h light period, 18 °C day temperature, and 15 °C night temperature. Treatments with or without a living rye cover crop were treated with either: (i) no manure; (ii) a phosphorus-based manure application rate (low manure): or (iii) a nitrogen-based manure application rate (high manure). We observed a significant reduction in N₂O emissions in the presence of the rye cover crop. Field experiments were performed on a fine-loamy soil in Central Iowa from October 12, 2005 to October 2, 2006. We observed no significant effect of the cover crop on cumulative N₂O emissions in the field. The primary factor influencing N₂O emission was N application rate, regardless of form or timing. The response of N₂O emission to N additions was non-linear, with progressively more N₂O emitted with increasing N application. These results indicate that while cover crops have the potential to reduce N₂O emissions, N application rate may be the overriding factor.     

A Water Allocation Decision‐Support Model and Tool for Predictions in Ungauged Basins in Northeast British Columbia,Canada

Pressures on water resources due to changing climate, increasing demands, and enhanced recognition of environmental flow needs result in the need for hydrology information to support informed water allocation decisions. However, the absence of hydrometric measurements and limited access to hydrology information in many areas impairs water allocation decision‐making. This paper describes a water balance‐based modeling approach and an innovative web‐based decision‐support hydrology tool developed to address this need. Using high‐resolution climate, vegetation, and watershed data, a simple gridded water balance model, adjusted to account for locational variability, was developed and calibrated against gauged watersheds, to model mean annual runoff. Mean monthly runoff was modeled empirically, using multivariate regression. The modeled annual runoff results are within 20% of the observed mean annual discharge for 78% of the calibration watersheds, with a mean absolute error of 16%. Modeled monthly runoff corresponds well to observed monthly runoff, with a median Nash–Sutcliffe statistic of 0.92 and a median Spearman rank correlation statistic of 0.98. Monthly and annual flow estimates produced from the model are incorporated into a map‐ and watershed‐based decision‐support system referred to as the Northeast Water Tool, to provide critical information to decision makers and others on natural water supply, existing allocations, and the needs of the environment.     

Effects of Pollinator Loss on Endemic New Zealand Mistletoes (Loranthaceae)

Abstract: The endemic mistletoes Peraxilla colensoi and P. tetrapetala (Loranthaceae) have declined considerably in New Zealand since 1840, reputedly because of introduced herbivores but coincident with a major decline in native bird densities. We show that at two South Island sites ( Craigieburn and Ohau) there are too few bird pollinators visiting the flowers to allow full fruit set. We studied pollination rates in P. colensoi at Wakefield and P. tetrapetala at Craigieburn over four flowering seasons and P. tetrapetala in one season at Ohau. Supplemental hand pollination increased fruit production 1.25–5.3 times at Craigieburn and Ohau but not at Wakefield. Excluding birds by covering mistletoes with mesh bags decreased fruit set significantly at Wakefield but had little effect at Craigieburn and Ohau. Bellbirds ( Anthornis melanura ) and Tuis (   Prosthemadera novaeseelandiae ) visited flowers significantly more often at Wakefield than at Craigieburn. A lack of pollen tubes in the style, not self-incompatibility or resource shortage, caused the low fruit production in unmanipulated flowers at Craigieburn. Thus, at the two P. tetrapetala sites (Craigieburn and Ohau) fruit set was chronically pollen limited, whereas P. colensoi at Wakefield was not pollen-limited. Data from other Peraxilla sites also suggest pollination failure. Our study suggests that the conservation of Peraxilla species will require maintenance of native bird populations. Tuis and Bellbirds are important pollinators and dispersers of many other New Zealand plants, and the breakdown of such mutualistic relationships may have widespread consequences.     

Sedentary or mobile? Variability in space and depth use of an exploited coral reef fish

Movement of fishes defines the distribution and abundance of populations and occurs on a range of spatial and temporal scales. To successfully parameterise assessments and design management strategies for exploited fish populations, knowledge and consideration of their movement patterns are essential. Since the efficacy of management approaches vary depending on the sedentary or mobile nature of the target species, presence, space use and depth utilisation were examined to understand the movement patterns of redthroat emperor Lethrinus miniatus. Sixty individuals were monitored for up to 12 months in an acoustic array comprising three coral reefs, and variation in space use and movement patterns was observed among 26 individuals. Half of the individuals were recorded only in proximity of one receiver along the reef edge, while the other half were detected at multiple receivers and used horizontal areas of approximately 4 km². Periods of non-detection and lower detection frequency at night (χ ₁ ²  = 342.157, P < 0.001) indicated individuals may move away from the monitored reef edge to the adjacent sandy habitat, but most movements outside the array remain unknown. Long-distance movement was recorded for one individual, recaptured ~160 km from the release location. Generally, no trends in depth use were apparent, L. miniatus inhabited a variety of depths, which were not related to individual size or time of day, yet some effect of month was evident. Variation in movement among adult L. miniatus indicates that while some individuals undergo broader-scale movement, spatial closures that cover individual reefs (>4 km²) could provide protection from fishing for the proportion of the population that displayed high site fidelity and moderate-sized activity spaces (over a period of up to 12 months).     

Diversity,abundance, and distribution of reef sharks on outer-shelf reefs of the Great Barrier Reef,Australia

Quantifying the distribution and habitat use of sharks is critical for understanding their ecological role and for establishing appropriate conservation and management regimes. On coral reefs, particularly the Great Barrier Reef (GBR), little is known regarding the distribution of sharks across major reef habitat types. In this study, we surveyed shark populations across outer-shelf reefs of the GBR in order to determine the diversity, abundance, and distribution of reef sharks across three major coral reef habitats: (1) the reef slope, (2) the back reef and (3) the reef flat. Model selection revealed that habitat was the principal factor influencing shark distribution and abundance. Specifically, overall shark abundance and diversity were significantly higher on the reef slope (and to a lesser degree, the back reef) than the reef flat. This confirms that shark populations are not homogeneously distributed across coral reefs. Thus, the results presented herein have important implications for shark population assessments. In addition, our results highlight the potential importance of the reef slope, with high levels of live coral cover and structural complexity, for sustaining reef shark populations. As this habitat is highly susceptible to disturbance events, this study provides a useful context for predicting and understanding how environmental degradation may influence reef shark populations in the future.