Olsen Ylva S.

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Olsen
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Ylva S.
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  • Article
    Macroalgal responses to experimental nutrient enrichment in shallow coastal waters : growth, internal nutrient pools, and isotopic signatures
    (Inter-Research, 2008-09-25) Teichberg, Mirta ; Fox, Sophia E. ; Aguila, Carolina ; Olsen, Ylva S. ; Valiela, Ivan
    Increased nutrient inputs to temperate coastal waters have led to increased occurrences of macroalgal blooms worldwide. To identify nutrients that are limiting to macroalgae and to determine whether different forms of these nutrients and long-term ambient nutrient conditions affect macroalgal response, we used in situ enrichment methods and tested the response of 2 bloom-forming species of macroalgae, Ulva lactuca and Gracilaria tikvahiae, from shallow estuaries of Waquoit Bay, Massachusetts, USA, that receive different land-derived N inputs. We enriched caged macroalgal fronds with nitrate, ammonium, phosphate, and N + P combinations, and measured growth, nutrient content, and δ15N signatures of fronds after 2 wk of incubation. In these estuaries, P did not limit growth, however, the 2 species differed in growth response to N additions. Growth of U. lactuca was greater in Childs River (CR), the estuary with higher nitrate inputs, than in Sage Lot Pond (SLP); growth in SLP increased with nitrate and ammonium enrichment. In contrast, growth of G. tikvahiae was greater in SLP than in CR, but had no growth response to N enrichment in either site. C and N contents differed initially between species and sites, and after nutrient enrichment. Final tissue % N increased and C:N decreased after nitrate and ammonium enrichment. δ15N values of the macroalgae demonstrated uptake of the experimental fertilizers, and a higher affinity and faster turnover of internal N pools with ammonium than nitrate enrichment in both species. We suggest that U. lactuca blooms in areas with both high nitrate and ammonium water column concentrations, and is more N-limited in oligotrophic waters where DIN levels are too low to sustain high growth rates. G. tikvahiae has a greater N storage capacity than U. lactuca, which may allow it to grow in less nutrient-rich waters.
  • Preprint
    Effect of field exposure to 38-year-old residual petroleum hydrocarbons on growth, condition index, and filtration rate of the ribbed mussel, Geukensia demissa
    ( 2007-10-06) Culbertson, Jennifer B. ; Valiela, Ivan ; Olsen, Ylva S. ; Reddy, Christopher M.
    In September 1969, the Florida barge spilled 700,000 L of No. 2 fuel oil into the salt marsh sediments of Wild Harbor, MA. Today a substantial amount, approximately 100 kg, of moderately degraded petroleum remains within the sediment and along eroding creek banks. The ribbed mussels, Geukensia demissa, which inhabit the salt marsh creek bank, are exposed to the spilled oil. Examination of short-term exposure was done with transplantation of G. demissa from a control site, Great Sippewissett marsh, into Wild Harbor. We examined the effects of long-term exposure with transplantation of mussels from Wild Harbor into Great Sippewissett. Both the short- and long-term exposure transplants exhibited slower growth rates, shorter mean shell lengths, lower condition indices, and decreased filtration rates. Our results add new knowledge about long-term consequences of spilled oil, a dimension that should be included when assessing oil-impacted areas and developing management plans designed to restore, rehabilitate, or replace impacted areas.