Dynamics of Submerged Aquatic Vegetation in the Patos Lagoon estuary

Study Extent

The studied meadow covers approximately 1000m2 from a shallow estuarine area (mesomixohaline region) of the Patos Lagoon estuary. The sampling design aims to cover the center of the meadow and their edges. The meadow is surveyed monthly along a 450m fixed transect. The meadow is marked in six fixed positions, with fixed wodden posts buried into the sediemt. The transect line is parallel to the coast, distant 500m of an estuarine Island (Pombas Island). This site has been continuously monitored since January 2000. The data inserted in the data basis covers the monthly average, from Janaury 2000 to May 2016.

Sampling

Sampling description: The SAV was monthly monitored within a meadow in six points along a 450m transect area. The transect is 450 m long and about 2 m wide In each sampling area, the percentage cover of macroalgae were visually estimated within 25x 25 cm quadrats (N=3). The SAV biomass were sampled by using cylindrical cores, buried into the sediment (ø 10cm, 15 cm depth) (N=3 per plot; total N=18). The samples were previously washed in the field with the help of sieves, packed and transported to the laboratory with ice. In the laboratory, the biomass samples are washed and cleaned from sediments, debris and associated fauna. The plant biomass is divided into their functional groups: rooted plants, macroalgae and epiphyte algae. The rooted plants are divided into bellowground and aboveground fractions. Plant development and phenology is also recorded. Epiphyte algae are removed from the leaves, by scraping the leaves with a surgical blade. Several demographic parameters are obtained for the rooted plants such as: hast length, leaves length, number of shoots, total rhizome length, number of nodes along the rhizome. The dry weight (48 h at 60°C) is obtained for Ruppia maritima (bellowground and aboveground) and for the group of macroalgae. Taxonomical analyses of macroalgal were performed by thallus anatomy using stereomicroscopy and optical microscopy.

Quality Control

Samples were collected by the Project Coordinator, Post-Docs, Post-Graduate and trainned undergraduated students. The methodoligical approach and methods were the same along during the 16 years time. The quality of data was checked monthly by the VAS Project Coordinator.

Method steps

1. SAV (plants and macroalgae) is surveyed for cover, biomass and demographic parameters. In the field, the presence of the meadow and the percentage cover is visually estimated. The plants are manually collected by cores, stored in refrigerator and analysed in 2 to 5 days. Plant dry biomass ad organic matter is obtained.

1. Ruppia maritima
   rank: species
2. Plantae
   rank: kingdom
3. Viridiplantae
   rank: subkingdom
4. Tracheophyta
   rank: phylum
5. Chlorophyta
   rank: phylum
6. Rodophyta
   rank: phylum
7. Monocots
   rank: class
8. Ulvophyceae
   rank: class
9. Florideophyceae
   rank: class
10. Alismatales
    rank: order
11. Ulvales
    rank: order
12. Cladophorales
    rank: order
13. Acrochetiales
    rank: order
14. Ceramiales
    rank: order
15. Ruppiaceae
    rank: family
16. Ulvaceae
    rank: family
17. Cladophoraceae
    rank: family
18. Acrochaetiaceae
    rank: family
19. Rhodomelaceae
    rank: family
20. Ruppia
    rank: genus
21. Ulva
    rank: genus
22. Rhizoclonium
    rank: genus
23. Cladophora
    rank: genus
24. Chaetomorpha
    rank: genus
25. Rhizoclonium
    rank: genus
26. Polysiphonia
    rank: genus
27. Acrochaetium
    rank: genus
28. Ulva intestinalis
    rank: species
29. Ulva compressa
    rank: species
30. Ulva clathrata
    rank: species
31. Ulva ramulosa
    rank: species
32. Ulva sp
    rank: species
33. Rhizoclonium riparium
    rank: species
34. Cladophora ssp
35. Chaetomorpha antennina
    rank: species
36. Chaetomorpha sp
    rank: species

The Patos Lagoon at the extreme southern Brazilian coastal plain (Rio Grande do Sul State) is the largest (10,360 km2) choked lagoon in the world and second largest lagoon in South America. The lagoon streches along 290 km long in a NE-SW direction, between the city of Porto Alegre (30º30’ S) and Rio Grande (32º12’ S). In the southern estuarine region, approximately 10 % of total area, a single and narrow inlet connects this lagoon to the Atlantic Ocean. The major tributary rivers at the northern and central areas of Patos Lagoon, and the São Gonçalo channel at the southern area, are significant freshwater sources from an extensive drainage basin. The hydrodynamics of Patos Lagoon estuary is strongly controlled by the discharge of tributary rivers and the action of predominant meteorological factors like winds, rainfall and evaporation.