Environmental impacts of dredging on seagrasses: a review.

Marine macrophyte biomass production, burial, oxidation, calcium carbonate dissolution, and metabolically accelerated diffusion of carbon dioxide across the air-sea interface may combine to sequester at least 10(9) tons of carbon per year in the ocean. This carbon sink may partially account for discrepancies in extant global carbon budgets.

http://science.sciencemag.org/content/sci/211/4484/838.full.pdf

Marine macrophytes as a global carbon sink.

Aim To produce an inventory of south-west Atlantic saltmarshes (from latitude 31°48′ S to 43°20′ S) using remotely sensed images and field sampling; to quantify their total area; to describe the biogeographical variation of the main habitats characterized by dominant vascular plants, in relation to major environmental factors; to test the hypothesis of predominance of the reversal pattern in plant distribution (sedges and grasses dominate the lower, regularly inundated zones, while the upper zones are occupied by more halophytic species) previously described; and to compare these south-west Atlantic saltmarshes with others world-wide.



Location  South-western Atlantic saltmarshes



Methods  Field samples of dominant emergent plant species positioned by the global positioning system (GPS) were obtained from most coastal saltmarshes (14) between southern Brazil and northern Patagonia, Argentina. Landsat satellite images were obtained and coastal saltmarsh habitats were quantified by supervised classification, utilizing points gathered in the field.



Results  Three main plant species dominated the low and middle intertidal saltmarsh, Spartina alterniflora Loesel., Spartina densiflora Brong. and Sarcocornia perennis (P. Mill.) A.J. Scott. The total area of the studied coastal saltmarshes was 2133 km2, comprising 380 km2 of Sp. alterniflora marsh, 366 km2 of Sp. densiflora marsh, 746 km2 of Sar. perennis marsh and 641 km2 of brackish marsh (dominated by Juncus acutus L., Juncus kraussii Hochst., Scirpus maritimus L., Scirpus americanus Pers. and Phragmites australis (Cav.) Trin.). Cluster analysis showed three habitat types: saltmarshes dominated by (1) Sp. densiflora and brackish species,(2) Sp. alterniflora and Sar. perennis and (3) Sp.densiflora only. The analysis of abiotic variables showed significant differences between groups of habitats and coordinated gradients of the abiotic variables. The south-west Atlantic coast showed decreasing mean annual rainfall (1200 to 196 mm) and increasing mean tidal amplitude (  2.5 m) from latitude 31° to 43°.



Main conclusions  South-west Atlantic saltmarshes are globally important by virtue of their total extent. Remote sensing showed that the reversal pattern in plant distribution is not widespread. Indeed, south-west Atlantic saltmarshes are better characterized by the presence of the halophytic genera Spartina and Sarcocornia. Our results support the interpretation that south-west Atlantic saltmarshes constitute a class of temperate type (sensuAdam, 1990) with transitional characteristics between Australasian–South African saltmarshes and west Atlantic saltmarshes.

/pdf/distribution-of-saltmarsh-plant-communities-associated-with-21ll71zc2a.pdf

Distribution of saltmarsh plant communities associated with environmental factors along a latitudinal gradient on the south‐west Atlantic coast

Epiphyte-seagrass relationships with an emphasis on the role of micrograzing: a review

Estimates of carbon store and carbon accumulation rate in mangrove and saltmarsh are beset by issues of scale and provenance. Estimates at a site do not allow scaling to regional estimates if the drivers of variability are not known. Also, carbon accumulation within soils provides a net offset only if carbon is derived in-situ, or would not otherwise be sequestered. We use a network of observation sites extending across 2000 km of southeastern Australian coastline to determine the influence of geomorphic setting and coastal wetland vegetation type on rates of carbon accumulation, carbon store and probable sources. Carbon accumulation above feldspar marker horizons over a 10-year period was driven primarily by tidal range and position in the tidal frame, and was higher for mangrove and saltmarsh dominated by Juncus kraussii than for other saltmarsh communities. The rate of carbon loss with depth varied between geomorphic settings and was the primary determinant of carbon store. A down-core enrichment in d 13 C was consistent with an increased relative contribution of mangrove root material to soil carbon, as mangrove roots were found to be consistently enriched compared to leaves. We conclude that while surface carbon accumulation is driven primarily by tidal transport of allocthonous sediment, in-situ carbon sequestration is the dominant source of recalcitrant carbon, and that mangrove and saltmarsh carbon accumulation and store is high in temperate settings, particularly in mesotidal and fluvial geomorphic settings.

/pdf/allochthonous-and-autochthonous-contributions-to-carbon-3m3ay7ioit.pdf

Allochthonous and autochthonous contributions to carbon accumulation and carbon store in southeastern Australian coastal wetlands

Lake Joondalup is a shallow body of fresh water in a calcareous stable dune system 6 km from the ocean. The fringing and aquatic vegetation is described. Cation ratios resemble sea water apart from relatively high calcium, attributed to leaching from limestone. Seasonal changes in volume greatly affect ionic concentrations. A bloom of the green alga Dispora coincides with low volume and high ion levels. Total nitrogen is relatively high compared with phosphorus. The surrounding land is becoming urbanized, and the data provide a baseline for future reference.

The nutrients and plants of Lake Joondalup, a mildly eutrophic lake experiencing large seasonal changes in volume

(1) The standing crop and productivity of the main primary producers (the sources of autochthonous detritus) were measured in a West Australian estuary which has a shallow estuarine basin, two small lagoons and a tidal river, and which has marked seasonal changes in salinity.
(2) Standing crops of phytoplankton (mainly diatoms) are small in the open water; no blooms were observed during 3 yr. In sporadic sampling the highest concentration of chlorophyll 'a' was 1-98 jig I -1. Sediments contain more chlorophyll (as microscopic algae) per unit area than does the water column. Small phytoplankton stocks are attributed to low nutrient concentration when light flux and temperature are high and water-residence time low.
(3) Macroscopic algae (twenty species) are most prominent in the summer marine phase. Their distribution is very patchy, and they have a small total biomass. 
(4) There are four benthic angiosperms in the estuary. The greatest contributor to production in open water is Ruppia, which is the most widely distributed of these, and has a peak dry-weight standing crop of 503 g m-2.
(5) The fringing marshes are mainly dominated by Juncus kraussii, which reaches a dry-weight standing crop of about 5 kg m-2.
(6) Based on general distribution, standing crops and published seasonal data, it is estimated that Ruppia produces about 700-1900 tonnes (dry weight) yr- 1, Juncus about 1000-4500, and the paperbark trees (Melaleuca spp.) of the marsh about 800 tonnes yr- 1 in leaf litter. Most of this organic material must become available as detritus, as only Ruppia is grazed appreciably.

The vegetation of the Blackwood River estuary, southwest Australia

There is little published information about coastal salt marshes in south-western Australia, which are prominent in estuaries but absent from the high energy coastline. The zonation of the marshes of the Blackwood estuary resemble those in other parts of the world, in that Sarcocornia marsh occurs near the mouth, followed by rush marsh, with sedges further upstream, suggesting that salinity is a prime determining factor. Spartina and Phragmites are absent. The most exensive marsh is the Juncus kraussii rush community which is invaded by the paperbark tree, Melaleuca cuticularis. The sedge Baumea juncea forms a marsh community on the shores of the lower tidal river and a progression of species occurs with distance along the tidal river. A number of dynamic processes observed in these marshes are described and related to observations elsewhere

Zonation in the marsh vegetation of the Blackwood River Estuary in south‐western Australia

Paperbark low closed forest, dominated by Melaleuca cuticularis, produced 430 g (dry weight), m−2 of litter over a year, containing some 3.4 g.m−2 of nitrogen and 77 mg.m−2 of phosphorus. Twigs and bark made up more than 50% of the total annual litter fall. The twigs and bark contribute most of the nitrogen (54 %) and phosphorus (56%), compared with leaf fall (37% and 35%) and flower and fruit fall (8% and 9%). The fall of leaves, twigs and bark was primarily related to wind, and flower and fruit fall was greatest after flowering. The litter must make a significant contribution to the accretion of peat. Since the forest covers some 200 ha of the lower Blackwood River estuary, it may contribute some 8001 of litter to the ecosystem each year, containing some 6600 kg of nitrogen and 154 kg of phosphorus.

Litter fall of the paperbark tree (Melaleuca cuticularis) in the marshes of the Blackwood River Estuary, Western Australia

Productivity of Ruppia: Seasonal changes and dependence on light in an Australian estuary

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