Developing an independent, generic, phosphorus modelling component for use with grid-oriented, physically-based distributed catchment models
KeywordGrid oriented phosphorus component
MetadataShow full item record
StatisticsDisplay Item Statistics
AbstractGrid-oriented, physically based catchment models calculate fields of various hydrological variables relevant to phosphorous detachment and transport. These include (i) for surface transport: overland flow depth and flow in the coordinate directions, sediment load, and sediment concentration and (ii) for subsurface transport: soil moisture and hydraulic head at various depths in the soil. These variables can be considered as decoupled from any chemical phosphorous model since phosphorous concentrations, either as dissolved or particulate, do not influence the model calculations of the hydrological fields. Thus the phosphorous concentration calculations can be carried out independently from and after the hydrological calculations. This makes it possible to produce a separate phosphorous modelling component which takes as input the hydrological fields produced by the catchment model and which calculates, at each step the phosphorous concentrations in the flows. This paper summarise the equations and structure of Grid Oriented Phosphorous Component (GOPC) developed for simulating the phosphorus concentrations and loads using the outputs of a fully distributed physical based hydrological model. Also the GOPC performance is illustrated by am example of an experimental catchment (created by the author) subjected to some ideal conditions.
FunderEnvironmental Protection Agency; Teagasc
Showing items related by title, author, creator and subject.
Farm-gate phosphorus balances and soil phosphorus concentrations on intensive dairy farms in the south-west of IrelandRuane, E. M.; Treacy, M.; McNamara, K.; Humphreys, James (Teagasc (Agriculture and Food Development Authority), Ireland, 2014)Phosphorus (P) loss to water is a significant threat to water quality in Ireland. Agriculture is an important source of this P. There is concern about balancing agronomic requirements and environmental protection in regulations prescribing P management on farms. This study examined farm-gate (P) balances and soil test P (STP) concentrations on 21 dairy farms in the south west of Ireland over four years, from 2003 to 2006 inclusive. Stocking density on the farms averaged 2.4 (s.d. = 0.4) livestock units (LU) per ha. Annual mean import of P onto farms was 21.6 (1.9) kg P/ha. Fertilizer P accounted for 47% (0.041), concentrates 35% (0.060) and organic manures 18% (0.034) of imported P. The mean annual P balance per farm was 9.4 (1.2) kg/ha, ranging from –3 to 47 kg/ha and mean P use efficiency was 0.71 (0.05) ranging from 0.24 to 1.37. The mean STP per farm following extraction using Morgan’s solution was 8.15 (2.9) mg/L of soil and ranged from 4.4 (2.2) to 14.7 (6.4) mg/L. There was a positive relationship (R2 = 0.34; P < 0.01) between STP and P balance; farms with a deficit of P tended to have agronomically sub-optimal STP and vice versa. The high between- and withinfarm variation in STP indicates that farmers were either unaware or were not making efficient use of STP results, and consequently there was agronomically sub-optimal soil P status in some fields and potentially environmentally damaging excesses on others (often within one farm). There was considerable potential to improve P management practices on these farms with clear agronomic and environmental benefits.
An assessment of the long-term effects of three phosphorus fertiliser regimes on soil phosphorus and sward condition.Culleton, Noel; Murphy, W.E.; Carton, Owen T.; Cuddihy, A. (Teagasc, 1999-04-01)A grazing trial using beef animals (mean weight 260 kg) was used to determine optimum soil phosphorus levels for dry stock farming. · The trial commenced in 1968. There were three fertiliser P treatments, 0, 15 and 30 kg P/ha applied annually. There were two stocking rates, 3300 and 2400 kg liveweight at turn out, respectively. Animals were rotationally grazed around six paddocks per treatment and stocking rates were reduced in June and September to match feed supply. The trial continued until 1998. ¸ Nitrogen was applied at a rate of 220 kg/ha per year to all treatments. ¹ Liveweight gains/ha/year were monitored annually. Soil P levels were monitored by sampling to 10 cm depth. º The distribution of phosphorus in the soil was recorded by analysing P levels at various depths from 0-2 mm to 100 cm. Botanical composition was recorded at the commencement of the trial and again in 1997. Phosphorus levels in herbage were also recorded. » An analysis of the liveweight gain data showed that for optimum output a Soil Index of 3 (Morgans P between 6.1 and 10.0 mg/l) is the target Soil P Index. ¼ Phosphorus recovery (as expressed by percentage of P fertiliser recovered in product) in the P30 treatments was low and was better in the P15 treatments. ½ The vast bulk of P accumulated near the surface of the soil, but there was some evidence of movement down the profile in the P30 treatment over a 30 year period. The soil P status influenced both the botanical composition of the sward and the P content in the herbage. The perennial ryegrass content declined on the zero P treatment, while there were no significant differences between the P15 and P30 treatments. The P concentration in the herbage in the zero P treatments were not sufficient for healthy growth of plants or animals.
Eutrophication from agricultural sources : a comparison of SWAT, HSPF and SHETRAN/GOPC phosphorus models for three Irish catchments - Final ReportNasr, Ahmed Elssidig; Bruen, Michael (University College Dublin. Centre for Water Resources Research, 02/07/2012)Phosphorous has been implicated as the primary cause of the deterioration of surface water quality in Ireland. Extensive water quality surveys revealed that diffuse sources (runoff and subsurface flows) from agricultural land are the major contributors of phosphorus to surface waters. The mechanism of phosphorus movement from land to water can be described by a number of mathematical models that vary in modelling approaches and scales (plot, field and catchment). In this work three efficient mathematical models of diffuse source pollution in general and of phosphorus in particular have been applied, for the first time, to three Irish catchments (Clarianna (Co. Tipperary), Dripsey (Co. Cork) and Oona (Co. Tyrone)) in order to explore the suitability of these models in Irish conditions for future use in implementing the European Water Framework Directive (WFD). The models are: (i) Soil Water Assessment Tool (SWAT), (ii) Hydrological Simulation Programme FORTRAN (HSPF) and (iii) Système Hydrologique Européen TRAnsport (SHETRAN). The first two can model phosphorus production directly while the third can calculate fields of various hydrological variables relevant to phosphorous modelling. For the latter, a generic phosphorus modelling component called Grid Oriented Phosphorus Component (GOPC) has been developed here to model the phosphorus detachment and transport by taking as inputs the hydrological fields produced by any physically-based distributed catchment model such as SHETRAN. The three models have been successfully transferred to Irish conditions and this required the build up of a database consisting of topographic, land use and soil maps, water quality and weather data. The models application involved two stages. In the first stage, hydrological variables (evaporation, runoff, etc.) within the catchment domains were simulated by each of the three models. The second stage uses the outputs of the first in order to estimate the amount of phosphorus loss from the catchments. The SWAT, HSPF, and SHETRAN/GOPC models have been calibrated and then compared and assessed on the basis of their ability to fit and reproduce the flow discharges and phosphorus loads and concentrations for the three test catchments. The findings from the flow and phosphorus calibrations of SWAT and HSPF models were generally consistence with what have been found from previous studies outside Ireland. However, the simple structure of the first order kinetics method used for phosphorus modelling in HSPF has generally impeded the freedom of the phosphorus calibration which was noticeably difficult. Application of the SHETRAN model to the study catchments has illustrated the importance of carefully assigning the parameters related to the soil water modelling, particularly the parameters of the van Genuchten soil-hydraulic function, in order to obtain the best results. The GOPC performance has been found to depend significantly on the SHETRAN model which provided the required hydrological variables. The flow comparison has showed that in the three catchments, the HSPF model was the best in simulating the mean daily discharges. Moreover discharge simulation from an independent validation run of the three models in the Oona catchment have also demonstrated the superiority of the hydrological component of HSPF. However, the best calibration results for daily total phosphorus loads in the study catchments has been achieved by the SWAT model. However from the validation in the Oona catchment the HSPF has been found better than the other two models, SWAT and GOPC, in simulating the total phosphorus loads. Generally the results of total phosphorus loads from the GOPC in the three catchments were quite good and this model has reproduced some observed values better than the best model, SWAT. Simulation of the daily dissolved reactive phosphorus loads by the three models in the study catchments have showed big differences between the simulated and the observed data in most of the cases. Results for mean daily total and dissolved reactive phosphorus concentrations from the three models were not as good as the results for the loads in the three catchments.