**7. Sediment and water interaction**

*Lagoon Environments Around the World - A Scientific Perspective*

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**Figure 10.**

*N. vitrea* var. *salinarum*, *Rhopalodia runrichiae*, and *Terpsinöe americana* (**Table 2**). In agreement with other studies, the epipsammic fraction appeared to be much

*I. A. maracaiboensis. II. Amphora sp. 2. III. A. ectorii. IV. Halamphora coffeaeformis. V. Rhopalodia runrichiae. VI. Opephora pacifica. VII. O. aff. mutabilis. VIII,IX. Erhembergia granulosa. X. Fallacia subforcipata. XI. F. florinae. XII. Placoneis elegantula. XIII. Navicula phylleptosomaformis. XIV. Seminavis strigosa. XV. Nitzschia frustulum. XVI. N. palea. XVII. N. scalpelliformis. XVIII,XIX. Cocconeis euglypta. XX,XXI. C. sawensis. XXII. Luticola simplex. XXIII. Catenula adhaerens. XXIV-XXVII. Fragilaria eichhornii. XXVIII. Diploneis didyma. XXIX. D. litoralis var. clathrata. XXX. D. interrupta. XXXI. D. smithii. Scale bar = 10 µm.*

more stable than epipelic assemblage [9, 67].

We expected to find planktonic forms in the sediment due to the low depth of the lagoon and because of the fact that the sediment usually integrates planktonic and periphytic taxa [3]. The absence of planktonic forms could be explained by the hydrographic processes that tend to transport nonliving, unattached forms out of the system, similar to estuaries [67]. Furthermore, the location of the sampling stations, since the material was collected on the lagoon margin, was outside the water surface. However, it is known that in periods with decreasing wind intensity, water tend to return flooding areas that had been exposed [50]. A few planktonic species in the sediment were also recorded in a study of microphytobenthos in the Gulf of Trieste, Europe, although the collections were made in submerged sediment [65].

Comparing with an earlier study about phytoplankton at Peixe Lagoon, with sampling performed during the same period, *Asterionellopsis glacialis* (Castracane) Round, *Chaetoceros gracillis* Pantocsek, and *Skeletonema potamos* (Weber) Hasle were found in abundance in plankton samples. In this study, however, these species were not found in the sediment; whereas *Diploneis didyma*, a highlighted species found in benthos, was also present in the plankton. The species *Cocconeis sawensis* was recorded at the southern benthos of the lagoon, and it was also observed in the plankton and epiphyton in association with the macroalgae *Cladophora* sp. in the fall and winter seasons [33, 46]. This suggests that in shallow environments, the plankton receives a greater contribution of benthic species than the opposite. Similar results were found in shallow estuarine zone of Patos Lagoon [19].

Estuary and shallow coastal waters develop the process of resuspension whereby sediment particles with diatoms enter the water column. Examination of diatoms in the water revealed that 75% of frustules belonged to pennate forms and we concluded that flooding tides were responsible for a net transport of epipelic diatoms from the mudflat to a salt marsh. The resuspension of the diatoms can be the source of the chl *a* peak in the plankton [68]. So, this organism may greatly augment the primary production in water [69, 70]. Other investigations have showed large number of benthic diatoms in the water column [71, 72]. The wind, flooding tides, and tidal inducing waves and currents are the causes of this process.
