Nutrient dynamics in the intertidal pools of the Mondego estuary: I - nutrient sources, sediment profiles, mineralisation and absorption dynamics

During the last decades the Mondego estuary has been under severe ecological stress mainly caused by eutrophication. In this salt march system, Spartina maritima covers about 10.5 ha of the intertidal areas. The objective of the present study was to evaluate the effect of Spartina maritima marshes on the dynamics of phosphorus (P) binding in the surface sediment. We compare phosphate and oxygen fluxes, P-adsorption capacity, phosphate concentrations and total amount, and the extractable P forms in the upper 20 cm of sediment in vegetated sediment with adjacent mudflats without vegetation. Sediment pore-water profiles followed a clear trend, with lower P concentrations in more superficial layers, and increasing with depth. The vegetated mudflats presented lower concentrations of dissolved inorganic phosphorus than adjacent bare bottom mudflats, lower phosphate total amount, as well as higher P-adsorption capacity. Results from the extraction procedure show that the superficial layers are the most important for estuarine phosphorus dynamics, since maximum concentrations of labile P pools are present here. In contrast, higher proportions of refractory P pool are found in deeper layers. Spartina marsh sediments had less total P, less iron bound P, and less exchangeable P than adjacent bare bottom mudflats. Also the pool of loosely sorbed P is lower in the Spartina marsh. Phosphate regeneration from the sediment to the overlying water was only 11.8 kg ha -1 year -1 in vegetated sediment while 25.8 kg ha -1 year -1 in the bare mud flat. Plant uptake for growth combined with an enhanced P-adsorption capacity of the sediment, may explain these differences. Therefore, Spartina marshes are very important agents in the sedimentary P cycle worldwide, and can be considered a useful management tool in estuarine ecosystem recovery efforts.

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“…Vale et al, 1990;Warren and Niering, 1993;Christensen & Andersen, 1996;Sá nchez et al, 2001;Flindt et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Spartina maritima influence on the dynamics of the phosphorus sedimentary cycle in a warm temperate estuary (Mondego estuary, Portugal)

et al. 2007

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“…In general, salt marshes are considered as efficient sinks for nutrients, and in Spartina maritima rhizosphere, sediment storage capacity (namely for phosphorus) is enhanced by sediment accretion and sediment oxidation (Adam, 1990;Chambers and Odum, 1990;Sa´nchez et al, 2000;Flindt et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Phosphorus speciation and availability in intertidal sediments of a temperate estuary: relation to eutrophication and annual P-fluxes

Coelho

Flindt

Jensen

et al. 2004

Estuarine, Coastal and Shelf Science

161

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For a better understanding of the phosphorus dynamics and bioavailability in temperate climates, sequential chemical extraction techniques were used to study sediment P-pools distribution and relative importance in a eutrophicated estuary.Results indicate a shift in importance from the iron-bound P fraction to the CaCO 3 -bound P fraction with increasing salinity, which suggests a decrease in bioavailable P from the most inner part of the estuary seaward, as the CaCO 3 associated P is believed to be less available for organisms. Salt marsh plants also influence sediment P speciation, through higher organic P fractions (mainly humic acid associated P) when compared to non-vegetated sediments. The ratio of iron-bound P to iron-oxyhydroxides may be used as an indicator of P availability, since it reflects the number of available P sorption sites in the metal oxides. This ratio was lowest in the intermediate zone of the estuary (13.7) when compared to the outer site (29.6) and the upper site (26.1), suggesting saturation of sorption sites. Co-incident with this, the intermediate site is characterized by the occurrence of macroalgal blooms during summer. In the present case, superficial sediments in the Mondego estuary do not show a clear seasonal trend, either in total amounts of exchangeable P or P speciation. Pools of exchangeable P in the surface sediment were w30 times higher than the annual net-export of P (14 ton year ÿ1 ) from the estuary. The annual P release from the sediment appears diminutive in comparison with the pool-size. Management measures to reduce nutrient input into coastal water systems should therefore consider that phosphorus availability may persist as a result of sediment supply, even after reducing the external point sources.

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“…Biota living in the intertidal zone of mesotidal and macrotidal estuaries and coastal embayments are adapted to a dynamic environment dominated by the tidal flooding and ebbing (Widdows and Brinsley, 2002). During tidal ebbing extensive areas of sand-and mudflats are covered by several low water pools (Flindt et al, 2002). During exposure of the tidal flats important biogeochemical processes take place in these ephemeral pools as a result of anabolic/catabolic balances, and of a combination of shallow water and enhanced temperature (Flindt et al, 2002;Lillebø et al, 2002a,b).…”

Section: Introductionmentioning

confidence: 99%

“…During tidal ebbing extensive areas of sand-and mudflats are covered by several low water pools (Flindt et al, 2002). During exposure of the tidal flats important biogeochemical processes take place in these ephemeral pools as a result of anabolic/catabolic balances, and of a combination of shallow water and enhanced temperature (Flindt et al, 2002;Lillebø et al, 2002a,b). The size of these pools may vary from some square centimetres to a few square metres.…”

Section: Introductionmentioning

confidence: 99%

“…Plant roots have complex interactions with the surrounding sediment, covering a wide range of biogeochemical processes, namely changes in the rhizosphere chemistry, including the redox potential (Eh), organic matter content, metal availability and also the nutrient profiles (e.g. Cac xador et al, 1996Cac xador et al, , 2000Cartaxana and Lloyd, 1999;Flindt et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

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Phosphorous dynamics in a temperate intertidal estuary

Lillebø¹,

Neto²,

Flindt³

et al. 2004

Estuarine, Coastal and Shelf Science

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Conservation and management of aquatic systems require detailed information of the processes that affect their functioning and development. The objectives of the present work were to describe the phosphorus dynamics during a complete tidal cycle and to quantify the relative contribution of the most common estuarine areas (e.g. seagrass beds, salt marshes, mud-and sand-flats without vegetation) to phosphorus net internal loading in a temperate intertidal estuary. Results show that phosphate efflux rates were higher during the first hours of tidal flood, and that phosphate concentrations were lowest at high tide. During tidal ebbing, ephemeral tide pools may cover a considerable percentage of the intertidal area. In these tide pools, water shallowness combined with enhanced temperatures stimulate the occurrence of high phosphate effluxes. The effluxes to the main water body during high tide contributed 57% of dissolved inorganic phosphorus and efflux during low tide contributed 43% to the net internal loading. Calculations of the phosphate net effluxes (kg P) indicate a strong contribution of the bare bottom mud-flats to the whole system internal phosphate loading, especially during the warmer periods. As a consequence of eutrophication, perennial benthic macrophytes are commonly replaced by fast-growing epiphytic macroalgae. Calculations showed that for a hypothetical intertidal estuary in a temperate region, management programs considering an eventual re-colonization of mud-flats by seagrasses or salt marsh plants may reduce the P-efflux by 13e16 kg ha ÿ1. For example, in the small Mondego estuary, eutrophication has contributed to a reduction of the Zostera noltii meadows, leading to an increase in 190 kg of phosphorus net internal loading.

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Nutrient dynamics in the intertidal pools of the Mondego estuary: I - nutrient sources, sediment profiles, mineralisation and absorption dynamics

Cited by 3 publications

References 2 publications

Spartina maritima influence on the dynamics of the phosphorus sedimentary cycle in a warm temperate estuary (Mondego estuary, Portugal)

Spartina maritima influence on the dynamics of the phosphorus sedimentary cycle in a warm temperate estuary (Mondego estuary, Portugal)

Phosphorus speciation and availability in intertidal sediments of a temperate estuary: relation to eutrophication and annual P-fluxes

Phosphorous dynamics in a temperate intertidal estuary

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