Data set title:
Nutrient concentration profiles from long term time series at Station L4 in the Western English Channel from 2000 to 2012.

Name of data file:
nutrients_l4_2000-2012.csv

Data set creator(s) and institute(s):
E. Malcolm S. Woodward, Carolyn Harris and Lisa Al-Moosawi. Plymouth Marine Laboratory.

Data set period: 
2000-01-17 to 2012-12-18

Data set abstract:
Results are reported for the analysis of water samples taken from the L4 long-term sampling station (50°15.0'N; 04°13.0'W) situated of the south-west coast of England, United Kingdom.
The analyses are reported for Nitrate+Nitrite, Nitrite, Silicate and Phosphate concentrations. The data set begins in 2000 and since 2007 has been on a more regular almost weekly sampling protocol. A classical picture is seen of generally summer nutrient depletion and with higher winter of the Nitrate, Silicate and Phosphate, however particularly in wet summers like 2012 there is a big influence of the River Tamar and spikes of high nutrient loads are seen being introduced into this near-shore sampling site.

Sampling methodology and description of analytical techniques:
The nutrient samples for L4 are taken weekly where the conditions allow it. They are sampled under clean conditions, using gloves to avoid contamination, and are returned in the cool and dark, and as soon as possible, to the laboratory in Plymouth where triplicate samples are analysed both for filtered (0.2μm Millipore Fluoropore) and non-filtered water. This gives us essentially 'live' results and the results are processed and up-loaded onto the internet as soon as possible after analysis. Samples are not stored or frozen unless there are extenuating circumstances making the 'live' analysis impossible. 
The analyser is a 5-channel Bran and Luebbe segmented flow system using well tested colorimetric analytical methodologies (Woodward, E.M.S, and A.P. Rees, (2001). Nutrient distributions in an anticyclonic eddy in the North East Atlantic Ocean, with reference to nanomolar ammonium concentrations. Deep Sea Research II, 48, Nos. 4-5, 775-794), and the same as those used by the PML nutrient group in all their International Research cruises, and research programmes. Quality control procedures are carried out with regular use of KANSO certified reference materials, and also the group participates in the European Quasimeme programme as well as being a member of the International Nutrient Scale System International Intercalibration programme steering committee. 
The live analytical protocol has been in existence since 2007 and the studies are part of the UK National Capability programme of the Western Channel Observatory. Prior to 2007 the samples were stored frozen and then analysed in batches.

Data quality comments:
The data has all been Quality Controlled, and since 2007 when the freezing storage was discontinued the data will be a lot more reliable as freezing can cause contamination issues with sample concentrations. Since 2007 the samples have in general been analysed 'live' and without storage so the authors are more confident in those reported concentrations. Despite this caveat, the year on year trends show a good consistent pattern since the beginning of this sampling programme. 

Data usage:
It is essential for all users of these data to establish and maintain contact with the nominated current data originators as well as fully consulting the metadata. While not impinging on free data access, this ensures that this dataset is being used in the correct way, and any potential issues with the data are clarified. As more samples are identified, a proper dialogue with these local experts on the series may enable, where appropriate the most recent dataset to be used.