Dynamics of Ammonia Exchange in Response to Cutting and Fertilising in an Intensively-Managed Grassland

Continuous micrometorological measurements of ammonia (NH₃)exchange were made for a period of 19 months (May 1998–November 1999) over intensively managed grassland in southern Scotland. This study focused on the influence of management activities, such as cutting and fertilising, on vegetation-atmosphere exchange of NH₃. Measurements were conducted within the European project GRAMINAE (GRassland AMmonia INteractions Across Europe) within which the Scottish site forms one of 6 sites in an E–W transect across Europe. NH₃ emissions were enhanced (up to 300 ng m^-2 s^-1) after cutting followed by larger emissions after fertilising (up to 1400 ng m^-2 s^-1). Annual budget calculations show the intensive grassland acted as a net source (1.8 kg N ha^-1 yr¹) although fluxes were bi-directional with deposition dominating in the winter and emission in the summer. Initial modelling of the NH₃ exchange using a `canopy compensation point' model has been conducted for key periods. The dynamics of the fluxes during these key periods, such as before and after cutting and fertilising, may be reproduced by introducing different values of the apoplastic ratio, = [NH₄ ⁺]/[H⁺].     

Parameter values to model the soil ingestion pathway

Soil ingestion is an important exposure pathway for contaminants that are not otherwise very mobile in the environment. Health of both humans and animals can be affected. This paper summarizes the literature and recommends models and probabilistic parameter values for risk assessment applications. Models of the pathway require estimates of the amounts of soil ingested, the concentration of contaminants relative to the original soil, and the bioavailability in the gut of the contaminants ingested with soil. Using a lead-contaminated sandbox as an example, the modelling recommendations suggest that a child typically may consume 50 mg d^–1 of the sandbox soil, the soil ingested will have a tenfold higher lead concentration than the original soil, and the lead will be as bioavailable as if ingested as inorganic lead in water.The Canadian Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

The analysis of monitoring data with the aid of time-series analysis

Methods derived from time-series analysis are proposed for processing monitoring data. The necessity for the use of these methods is demonstrated. In a case study time-series analysis was applied to assess the impact of the closure of the Grevelingen estuary (S. W. Netherlands) in 1971 on a local wintering population of Oystercatchers (Haematopus ostralegus) in the adjacent Oosterschelde estuary.Communication No. 328 of the Delta Institute for Hydrobiological Research.     

Polynomial Surrogates for Open-Channel Flows in Random Steady State

Assessing epistemic uncertainties is considered as a milestone for improving numerical predictions of a dynamical system. In hydrodynamics, uncertainties in input parameters translate into uncertainties in simulated water levels through the shallow water equations. We investigate the ability of generalized polynomial chaos (gPC) surrogate to evaluate the probabilistic features of water level simulated by a 1-D hydraulic model (MASCARET) with the same accuracy as a classical Monte Carlo method but at a reduced computational cost. This study highlights that the water level probability density function and covariance matrix are better estimated with the polynomial surrogate model than with a Monte Carlo approach on the forward model given a limited budget of MASCARET evaluations. The gPC-surrogate performance is first assessed on an idealized channel with uniform geometry and then applied on the more realistic case of the Garonne River (France) for which a global sensitivity analysis using sparse least-angle regression was performed to reduce the size of the stochastic problem. For both cases, Galerkin projection approximation coupled to Gaussian quadrature that involves a limited number of forward model evaluations is compared with least-square regression for computing the coefficients when the surrogate is parameterized with respect to the local friction coefficient and the upstream discharge. The results showed that a gPC-surrogate with total polynomial degree equal to 6 requiring 49 forward model evaluations is sufficient to represent the water level distribution (in the sense of the \(\ell _2\) norm), the probability density function and the water level covariance matrix for further use in the framework of data assimilation. In locations where the flow dynamics is more complex due to bathymetry, a higher polynomial degree is needed to retrieve the water level distribution. The use of a surrogate is thus a promising strategy for uncertainty quantification studies in open-channel flows and should be extended to unsteady flows. It also paves the way toward cost-effective ensemble-based data assimilation for flood forecasting and water resource management.     

A Mathematical Model for the Effects of Fertilization on Nitrogen Concentrations in Unsaturated Soil on Blueberry Farms in Southern New Jersey

Nitrogen is commonly known as a food source for crops. However, the nitrogen compounds used in crop fertilizers, most commonly nitrate (NO₃) and ammonium (NH₄), are not widely understood. Blueberry plants do not take up these compounds as efficiently as organic nitrogen so varying amounts of leaching into the soil and groundwater will occur. A biogeochemical model consisting of ordinary and partial differential equations is implemented to computationally predict the concentrations of nitrate and ammonium in unsaturated soil of blueberry plants, specifically in the southern region of New Jersey. The model takes into account the type of soil of the region, the nitrate uptake of the plant, the water content in the roots region, the pressure heads in the soil pores, and the application rates of fertilizers containing nitrate, ammonium, and organic nitrogen. Computational simulations demonstrate that the model accounts for natural processes and, in addition, show that commonly used fertilizer application rates cause unnecessarily high concentrations of both nitrate and ammonium in the unsaturated soil level. Further, simulations show that decreasing nitrate fertilizer applications by 85.7% in annual and 91.8% in bi-annual schedules provides an optimal system for safe reapplication.     

Integration of modeling,monitoring and laboratory observation to determine reasons for air quality violations

An attempt was made to explain ambient air quality violations in the vicinity of industrial plants. Micrometeorology, diffusion calculaations, ambient readings, and plant engineering data are all taken into consideration to ascertain whether the plant is or is not the principal offender.Scrutiny of hi-vol filters using scanning electron microscopy for particle size analysis and particle chemical make-up as an assessment technique is also described.Case histories using the above analytical techniques are discussed.Presented at the 16th National Conference on Energy and the Environment, May 23, 1979     

In situ nitrogen enrichment experiments in two Idaho (U.S.A.) streams

We conducted a series ofin situ experimental nutrient additions in two Idaho streams: Deep Creek, a desert stream located in Southeastern Idaho, and Big Wood River, situated in a mountainous region of Central Idaho. In both streams, a homogeneous reach was partitioned into almost identical channels. This allowed us to vary nutrient levels and measure algal response in experiments uncomplicated by differences in other factors.Ammonium nitrate was added to the treatment channels in Deep Creek. After nine days,Cladophora glomerata still predominated in both the control and treatment channels and algal biomass was not statistically different between the two. In the Big Wood River experiment significant differences in chlorophylla concentrations were not detected among three treatments of differing nitrogen enrichment and the control for both natural and artificial substrates. Also chlorophylla levels were not correlated with nitrogen concentrations, and the composition of algal communities remained similar among all treatments.We conclude that macronutrient enrichment of streams does not necessarily result in an increase in algal density or a change in algal community structure so long as other factors, which may limit the use of nutrients by algae, remain unaltered. Our results suggest that light, current velocity, and macroinvertebrate grazing may account for the failure of the periphyton to respond toin situ additions of nitrogen (and phosphorus) in our study streams.     

Mercury in a northeastern Brazilian mangrove area, a case study: potential of the mangrove oyster Crassostrea rhizophorae as bioindicator for mercury

The Channel of Santa Cruz is a mangrove area in northeastern Brasil 40 km north of Recife. Until 1991 a chlor-alkali factory discharged large amounts of mercury into the main tributary of the channel, the Rio Botafogo. The objective of this study was to assess the potential of the mangrove oyster Crassostrea rhizophorae as a bioindicator for mercury in this area and to examine the influence of condition on mercury concentrations in the oysters. The investigation was carried out in the late rainy season (July to September) 1993, in the rainy season (April to June) 1994 and in the dry season (November/December) 1994. At 11 stations in the channel, mangrove oysters, surface sediments and suspended matter were sampled, representing different compartments of the system. The distribution of mercury in the Channel of Santa Cruz exhibited for all compartments the same distinct spatial pattern with maxima in the Rio Botafogo. Seasonal variations were small and revealed no clear tendencies. In addition, mangrove oysters were transplanted from more contaminated stations to less contaminated stations and vice versa. These experiments were designed to study the oysters' capability to adjust their mercury concentrations to a changing bioavailability of mercury. The transplantation experiments suggest that the oysters are capable to adjust to changing ambient mercury availability within a few months. The transplantation experiments also revealed the importance of condition changes on the mercury concentration of the oysters. This factor should not be ignored during pollution studies. However, condition had apparently no strong influence on the spatial or seasonal mercury variations of the oysters. The mangrove oyster is a suitable bioindicator for long-term changes in mercury availability. Received: 20 August 1997 / Accepted: 15 January 1998     

Manipulation of food and photoperiod promotes out-of-season gametogenesis in the green sea urchin, Strongylocentrotus droebachiensis: implications for aquaculture

Green sea urchins, Strongylocentrotus droebachiensis OF Müller, collected off the coast of New Hampshire, USA, in late February 1995, were brought into the laboratory and fed an artificial diet ad libitum, and subjected to a photoperiod advanced by 4 months. During this study, temperatures and salinities for experimental urchins mirrored those recorded at the collection site. We examined the effects of changes in feeding regime and photoperiod on gametogenesis and compared the experimental urchins with those from the source population. During the 7-month period, experimental urchins showed no detectable changes in mean test height or diameter. Experimental urchins had a significantly higher gonad index (GI) in March, April and May (18 ± 6%) compared with field urchins in March (11 ± 3%). Subsequently, experimental urchins had a mean monthly GI of 25 to 30%, while the mean GI for field urchins was 11 to 13%. Gonial cell mitosis and gametogenesis occurred earlier in experimental male and female urchins compared with field urchins. Stereological and histological observations and stage–frequency data showed that the ovaries of experimental urchins were large because of the accelerated development of nutritive phagocytes, the volume fraction (V _v) of which was 89 to 90% of the gonad, while new vitellogenic primary oocytes occupied <1% V _v. In males, stereological and histological observations and stage–frequency data suggested a mobilization of materials from the nutritive phagocytes beginning between June and August, i.e. earlier than in females, and, by September, new gametes occupied a V _v of 49 ± 3% of the testes. Oocyte size–frequency distributions demonstrated that most primary oocytes were <80 μm in diameter between March and September, suggesting that cold temperatures may be needed for completion of vitellogenesis. We describe changes in the two principal cell types in the germinal epithelium of urchin gonads and indicate how knowledge of their population dynamics may be useful in aquaculture applications. Received: 21 February 1997 / Accepted: 3 June 1998