PELD - ELPA | Isotopic and elemental composition of primary producers in the Patos Lagoon estuary

Study Extent

From March 2010 (austral summer) to June 2016 (autumn), estuarine primary producers were seasonally sampled in a mudflat and salt marsh edges off the Pombas Island, located in the mesomixohaline region of the Patos Lagoon estuary, southern Brazil.

Sampling

Estuarine primary producers were seasonally collected (N = 2-6) at the end of each season (i.e., March, June, September, December) in a mudflat in a shallow shoal off Pombas Island. Estuarine primary producers collected were: suspended particulate organic matter (POM; a proxy for phytoplankton and organic matter in the water column), particulate organic matter in the sediment (SOM; a proxy for microphytobenthos and organic detrital matter in sediments), drift macroalgae (Ulva spp. and Rhizoclonium spp.), the widgeon grass Ruppia maritima, and saltmarsh C3 (Scirpus maritimus and Scirpus olneyi) and C4 (Spartina densiflora) plants. Salt marsh plants were sampled at a regularly flooded low marsh. POM was obtained by filtering one liter of water onto a pre-combusted (450°C for 4 h) Whatman glass fiber filter (0.75 μm). SOM was obtained by removing the top 2 cm from the surface of the sediment using a core (10 cm diameter). Macroalgal thalli and seagrass and salt marsh plant leaves were manually collected, using scissors when necessary. All samples were stored in plastic bags and preserved on ice for transportation to the laboratory, where they were stored in a freezer until processing. Some gaps occurred in our seasonal data series (e.g., 2011-2012 and 2014-2015) due to logistical and financial constraints.

Quality Control

Material sampling and processing for isotopic and elemental were performed by researchers following the same procedures since the beginning of the time series. The samples were analyzed in the Analytical Chemistry Laboratory, University of Georgia, USA from 2010 through 2015 and in the Limnology Laboratory, University of North Texas, USA in 2016. The standard deviation between-laboratory revealed to be low and acceptable for comparing the isotope ratios for both carbon (SD=0.03‰, t=0.008, d.f.=8, p value= 0.993) and nitrogen (SD= 0.08‰; t=0.004, d.f.= 7.988, p-value=0.996). Taxonomic validity was verified using the World Register of Marine Species (WoRMS; www.marinespecies.org)

Method steps

1. In laboratory, plant samples were washed with distilled water, placed in sterile Petri dishes, and dried until constant weight (at 60ºC for 48h). The tissues analyzed were leaves and thalli filaments. The dried samples were ground to a fine powder with a mortar and pestle and stored in clean Eppendorf tubes. Aliquots of each dried sample (N = 2-6) were weighted (25-30 mg for SOM and ~ 3 mg for other basal sources), pressed into ultrapure tin capsules (Costech, Valencia, CA), and sent to the laboratory for analyses of total organic carbon (TOC), total nitrogen (TN) and carbon (13C/12C) and nitrogen (15N/14N) stable isotopes. SOM samples were not acidified prior to the analyses given the small carbonate content found in the sediment samples (average < 1%; maximum of 1.5%) compared to other benthic estuarine/marine environments. The stable isotope results were expressed in delta notation (the parts-per-thousand deviation from a standard material): δ13C or δ15N = [(Rsample/Rstandard) - 1] * 1000, where R = 13C/12C or 15N/14N. Standards were carbon in the Pee Dee Belemnite and nitrogen in air. TOC and TN values were expressed as percentages of plant dry weight.
2. Monitoring data was formatted according to the OBIS-ENV-DATA standard. Data presented in the Event Core (year-month) were not the exact sampling date, but an approximation representing each seasonal sampling event (see eventRemarks field). Due to the lack of taxonomic identification, POM and SOM data were presented as environmental measurements in the extended Measurement or Fact extension (extMoF). Distinct replicates for plants, SOM and POM were labelled using the measurementID field in the extMoF extension.

All plants were identified to the lowest taxonomic level possible. Scirpus spp. were comprised of Scirpus maritimus and Scirpus olneyi but isotopic and elemental data did not distinguish them. Macroalgae were drift mats of algae identified as Ulva spp. and Rhizoclonium spp. based on morphological attributes, however molecular analyses are necessary for taxonomic confirmation at species level. Macroalgae were thus grouped as Ulvophyceae.

1. Scirpus
   common name: salt marsh bulrush rank: genus
2. Spartina densiflora
   common name: cordgrass rank: species
3. Ruppia maritima
   common name: widgeon grass rank: species
4. Ulvophyceae
   rank: family

Estuarine primary producers were collected in a mudflat and salt marsh edges in a shallow shoal off Pombas Island. The area has been shown to be highly representative of the spatio-temporal dynamics of estuarine primary production and environmental conditions (i.e., parameters such as water salinity, temperature, turbidity, level and nutrient concentrations), and of the main ecological processes in the mesomixohaline region of the Patos Lagoon estuary