Document Detail

Temporal variability in nutrient concentrations and loads in the River Tamar and its catchment (SW England) between 1974 and 2004.
MedLine Citation:
PMID:  23054272     Owner:  NLM     Status:  Publisher    
This study reports the results from the analyses of a 30-year (1974-2004) river water quality monitoring dataset for NO( x )-N (NO(3)-N + NO(2)-N), NH(4)-N, PO(4)-P and SiO(2)-Si at the tidal limit of the River Tamar (SW England), an agriculturally dominated and sparsely populated catchment. Annual mean concentrations of NH(4)-N, PO(4)-P and SiO(2)-Si were similar to other rural UK rivers, while annual mean concentrations of NO( x )-N were clearly lower. Estimated values for the 1940s were much lower than for those of post-1974, at least for NO(3)-N and PO(4)-P. Flow-weighted mean concentrations of PO(4)-P decreased by approximately 60 % between 1974 and 2004, although this change cannot be unequivocally ascribed to either PO(4)-P stripping from sewage treatment work effluents or reductions in phosphate fertiliser applications. Lower-resolution sampling (to once per month) in the late 1990s may also have led to the apparent decline; a similar trend was also seen for NH(4)-N. There were no temporal trends in the mean concentrations of NO( x )-N, emphasising the continuing difficulty in controlling diffuse pollution from agriculture. Concentrations of SiO(2)-Si and NO( x )-N were significantly and positively correlated with river flows ≤15 m(3) s(-1), showing that diffuse inputs from the catchment were important, particularly during the wet winter periods. In contrast, concentrations of PO(4)-P and NH(4)-N did not correlate across any flow window, despite the apparent importance of diffuse inputs for these constituents. This observation, coupled with the absence of a seasonal (monthly) cycle for these nutrients, indicates that, for PO(4)-P and NH(4)-N, there were no dominant sources and/or both undergo extensive within-catchment processing. Analyses of nutrient fluxes reveal net losses for NO(3)-N and SiO(2)-Si during the non-winter months; for NO(3)-N, this may be due to denitrification. Areal fluxes of NO( x )-N from the catchment were towards the higher end of the range for the UK, while NH(4)-N and PO(4)-P were closer to the lower end of the ranges for these nutrients. These data, taken together with information on sestonic chlorophyll a, suggest that water quality in the lower River Tamar is satisfactory with respect to nutrients. Analyses of these monitoring data, which were collected at considerable logistical and monetary cost, have revealed unique insights into the environmental behaviour of key nutrients within the Tamar catchment over a 30-year period.
Alan D Tappin; Utra Mankasingh; Ian D McKelvie; Paul J Worsfold
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-11
Journal Detail:
Title:  Environmental monitoring and assessment     Volume:  -     ISSN:  1573-2959     ISO Abbreviation:  Environ Monit Assess     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-11     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8508350     Medline TA:  Environ Monit Assess     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, England, UK.
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