Artificial Top Layer Sediment Resuspension To Counteract Chaetomorpha Linum (Muller) Kutz Blooms In A Eutrophic Lagoon. Three Years Full-Scale Experience

Abstract

This study analyzes the full-scale results of a three-year eutrophication control and management in the Orbetello lagoon. We examined the cause/effect relationship among the resuspension of top layer sediment in the water column (carried out by specifically designated boats), the labile organic matter present in the sediments (LOM), and the values of Chaetomorpha linum high density mats, which insist in the disturbed areas. LOM values resulted inversely associated to the frequency of sediment disturbance. LOM decrease, together with higher oxidation levels, triggered the reduction of nutrient release with an immediate effect on algal masses: the decay of the mat under layer prevailed on the growth of the mat over layer. Conversely, with a reduced frequency of disturbance, and the consequent increase of both the LOM as well as the anaerobic processes of the sediment which promote nutrient releases, the algal growth showed a time lag of several months, in which the nutrients uptake was likely intense. The stored nutrients were then used only some months later, when the environmental conditions became favorable for the surprisingly rapid and impressive development of the mats.

C, N, P, S content of the Chlorophyta Chaetomorpha linum (Müller) Kützing in a vast high density mat of a Mediterranean non-tidal lagoon

“…3), which, in some areas, as a consequence of the wind pressure on the mat, exceeded 30 kg WW m −2 . Biomass also varied seasonally with winter minimums and spring maximums, to which must be added the effects of anthropic interventions that aimed to mitigate the problem (Lenzi et al, 2017), and more or less extensive summer dystrophic events. Consequently, LOM values were consistently very high (Tab.…”

“…C content showed a large fluctuation with periods of probable limitation, between June and October 2017, which could have led consequence of physiological stress, and with values of relative abundance, between July 2018 and April 2019. We have no data to establish the reasons for these fluctuations, however we must take into account that, in addition to the high densities, between 2014 and 2016 the mat was subjected to intense disturbance through the resuspension of the top layer sediment by boats (Lenzi et al, 2017), and to a heavy dystrophic event (Sorce et al, 2017), which may have contributed to the mat decline. Starting from 2017, the mat was restored, as soon as the anthropogenic pressure was reduced, showing a high resilience.…”

“…It was estimated that 6000 tonnes of macroalgae removed from the ecosystem involved the resuspension of over 15,000 tonnes of sediment (Lenzi et al, 2013b). From 2014, the main action to counter eutrophication has mainly been based only on direct resuspension of the sediment anoxic top layer (Lenzi et al, 2017). Sea-water pumping is still practiced Fig.…”

Zoobenthic Communities of a High-Density Mat of the Chlorophyta Chaetomorpha linum, in a Hypertrophic Lagoon

“…It was estimated that 6000 tones of macroalgae removed from the ecosystem involved the resuspension of over 15,000 tones of sediments . From 2014 to date, the action to counter eutrophication has mainly been based on the only direct resuspension of the anoxic sediment top-layer, with the aim of oxidizing the sediments and favoring the mineralization of labile organic matter (Lenzi et al, 2017). Sea-water pumping is still practiced annually, between June and August, to promote water turnover, through an input flow coming from two western pumping stations, at the lagoon-mouth of the two western canals (SLC 1, 2), and an output flow by the eastern canal (SLC 3; Fig.…”

Growth and physiological features of Chaetomorpha linum (Müller) Kütz. in high density mats

“…It thrives under eutrophic conditions, in particular with a high availability of orthophosphate (Lavery and McComb, 1991b;Menendez et al, 2002). The mats of this species may be particularly resilient and persistent (Gao et al, 2013;Lenzi et al, 2013Lenzi et al, , 2017.…”