Historical changes in oxygen concentrations along the Norwegian Skagerrak coast: Reply to the comment by Gray and Abdullah

Johannessen, Tore; Dahl, Einar

doi:10.4319/lo.1996.41.8.1847

Cited by 9 publications

(3 citation statements)

References 3 publications

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“…Oxygen concentrations typically display high variability due to climatic, physical, and biological factors. Interpretation of long‐term trends in oxygen concentrations is, consequently, frequently controversial (for example, see the debate between Gray and Abdullah [1996] and Johannessen and Dahl [1996] concerning historical changes in dissolved oxygen along the Norwegian coast). Long and reliable data records and methods to correct for climatic influences are ultimately required to resolve secular trends from transient effects.…”

Section: Hypoxia and Eutrophicationmentioning

confidence: 99%

Chesapeake Bay Eutrophication: Scientific Understanding, Ecosystem Restoration, and Challenges for Agriculture

2001

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Chesapeake Bay has been the subject of intensive research on cultural eutrophication and extensive efforts to reduce nutrient inputs. In 1987 a commitment was made to reduce controllable sources of nitrogen (N) and phosphorous (P) by 40% by the year 2000, although the causes and effects of eutrophication were incompletely known. Subsequent research, modeling, and monitoring have shown that: (i) the estuarine ecosystem had been substantially altered by increased loadings of N and P of approximately 7- and 18-fold, respectively; (ii) hypoxia substantially increased since the 1950s; (iii) eutrophication was the major cause of reductions in submerged vegetation; and (iv) reducing nutrient sources by 40% would improve water quality, but less than originally thought. Strong public support and political commitment have allowed the Chesapeake Bay Program to reduce nutrient inputs, particularly from point sources, by 58% for P and 28% for N. However, reductions of nonpoint sources of P and N were projected by models to reach only 19% and 15%, respectively, of controllable loadings. The lack of reductions in nutrient concentrations in some streams and tidal waters and field research suggest that soil conservation-based management strategies are less effective than assumed. In 1997, isolated outbreaks of the toxic dinoflagellate Pfiesteria piscicida brought attention to the land application of poultry manure as a contributing factor to elevated soil P and ground water N concentrations. In addition to developing more effective agricultural practices, emerging issues include linking eutrophication and living resources, reducing atmospheric sources of N, enhancing nutrient sinks, controlling sprawling suburban development, and predicting and preventing harmful algal blooms.

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Section: Hypoxia and Eutrophicationmentioning

confidence: 99%

Chesapeake Bay Eutrophication: Scientific Understanding, Ecosystem Restoration, and Challenges for Agriculture

2001

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“…Whereas many studies of coastal ecosystems have focused on impacts of cultural eutrophication (Jorgensen and Richardson, 1996), land-use changes and sediment in ux (Howarth et al, 1991) and hydrological changes (Swart et al, 1996a;, growing evidence suggests that estuarine ecosystems are also in uenced by climatic variability (i.e., Peterson et al, 1995;. With few exceptions, separating anthropogenic effects from those due to climatic causes has remained problematic due in part to the limited historical record available for most ecosystems (e.g., Johannessen and Dahl, 1996a;Gray and Abdullah, 1996;Swart et al, 1996a;Halley and Roulier, 1999).…”

Section: Introductionmentioning

confidence: 99%

Late-Holocene climate and ecosystem history from Chesapeake Bay sediment cores, USA

2003

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Abstract:Palaeoclimate records from late-Holocene sediments in Chesapeake Bay, the largest estuary in the USA, provide evidence that both decadal to centennial climate variability and European colonization had severe impacts on the watershed and estuary. Using pollen and dino agellate cysts as proxies for mid-Atlantic regional precipitation, estuarine salinity and dissolved oxygen (DO) during the last 2300 years, we identi ed four dry intervals, centred on ad 50 (P1/D1), ad 1000 (P2/D2), ad 1400 (P3) and ad 1600 (P4). Two centennial-scale events, P1/D1 and P2/D2, altered forest composition and led to increased salinity and DO levels in the estuary. Intervals P3 and P4 lasted several decades, leading to decreased production of pine pollen. Periods of dry midAtlantic climate correspond to 'megadroughts' identi ed from tree-ring records in the southeastern and central USA. The observed mid-Atlantic climate variability may be explained by changes in atmospheric circulation resulting in longer-term, perhaps ampli ed, intervals of meridional ow. After European colonization in the early seventeenth century, forest clearance for agriculture, timber and urbanization altered estuarine water quality, with dino agellate assemblages indicating reduced DO and increased turbidity.

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“…Norway has a heterogeneous coast comprising fjords, inlets, islets, skerries and variable depths. As a result, water temperatures, ocean current patterns, salinities and several other biotic and abiotic factors can be spatially structured at scales of less than a few kms (Johannessen & Dahl, 1996; Skjoldal, Hopkins, Erikstad, & Leinaas, 1995). This environment provides opportunities for species to adapt to local conditions at smaller spatial scales than the open ocean.…”

Section: Introductionmentioning

confidence: 99%

Cryptic microgeographic variation in responses of larval Atlantic cod to warmer temperatures

Oomen

et al. 2021

Preprint

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Although temperature is known to drive species dynamics and distributions, our understanding of the extent to which thermal plasticity varies within species is poor. Differences in plasticity can arise through local adaptation to heterogeneous environments, hybridization, and the release of cryptic genetic variation in novel environments. Here, wild Atlantic cod (Gadus morhua) from contrasting environments inside and outside of a fjord system in southern Norway spawned freely in a semi-natural laboratory environment, generating pure crosses and reciprocal hybrids. A common-garden rearing experiment of the larvae at 6°C, 9.5°C, and 13°C revealed cryptic genetic variation in thermal responses of growth and survival at warmer temperatures. Variation in growth plasticity was greatest from 9.5°C to 13°C, the latter of which exceeds temperatures currently typical of larvae in their native environments. In contrast to our prediction of intermediate hybrid responses consistent with additive genetic effects, one reciprocal hybrid cross showed a 4% increase in size at the highest temperature, whereas most crosses exhibited 4-12% reductions in size. All crosses experienced severe (76-93%) reductions in survival from 9.5°C to 13°C. Variation in survival plasticity suggests a genetically variable basis for the severity with which survival declines with increasing temperature and the potential for an adaptive response to warming. Notably, we demonstrate the potential for hybridization between coexisting 'fjord' and 'North Sea' ecotypes that naturally inhabit the inner and outer fjord environments at contrasting frequencies. Yet, ecotype explained a minor (3-10%) component of growth reaction norm variation, suggesting it is insufficient for describing important biological variation. Current broad-scale management and lack of coastal monitoring impede the development of strategies to maintain the potential for adaptation to warming temperatures in systems with such phenotypic complexity resulting from cryptic genetic variation, coexisting ecotypes, and gene flow.

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Historical changes in oxygen concentrations along the Norwegian Skagerrak coast: Reply to the comment by Gray and Abdullah

Cited by 9 publications

References 3 publications

Chesapeake Bay Eutrophication: Scientific Understanding, Ecosystem Restoration, and Challenges for Agriculture

Chesapeake Bay Eutrophication: Scientific Understanding, Ecosystem Restoration, and Challenges for Agriculture

Late-Holocene climate and ecosystem history from Chesapeake Bay sediment cores, USA

Cryptic microgeographic variation in responses of larval Atlantic cod to warmer temperatures

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