Long‐term trends in eutrophication and nutrients in the coastal zone

Abstract

We used high‐resolution paleoecological records of environmental change to study the rate and magnitude of eutrophication over the last century in two contrasting coastal ecosystems. A multiproxy approach using geochemical and biological indicators and diatom‐based transfer functions provides a long‐term perspective on changes in nutrient concentrations and the corresponding biological and sedimentary responses. In Roskilde Fjord, Denmark, total nitrogen (TN) increased 85% during the last century, with the most rapid increase occurring after the 1950s, corresponding to the postwar increase in N fertilizer use. In Laajalahti Bay, an urban embayment near Helsinki, Finland, total dissolved nitrogen (TDN) increased with growing wastewater inputs and decreased with the remedial actions taken to reduce these discharges. These changes are small relative to the order of magnitude increases in nutrient loading that have occurred in northwestern Europe, where the dissolved inorganic nitrogen (DIN) load has increased more than threefold in certain areas.

Historical records of coastal eutrophication-induced hypoxia

“…In area column B = Baltic; D = Denmark; F = Finland; N = Norway; S = Spain; Fla = Florida; Mx = Mexico. See Brush (2001), Cronin and Vann (2003), Kemp et al (2000) and Rabalais et al (2007) Andrén et al (1999); 7) Barmawidjaja et al (1995); 8) Blackwelder et al (1996); 9) Bratton et al (2003) ; 10) Brunner (2006); 11) Cearreta et al (2000); 12) Chen et al (2001); 13) Chmura et al (2004); 14) Clarke et al (2003); 15) Clarke et al (2006); 16) Colman and Bratton (2003); 17) Cooper (1995); 18) Brush (1991, 1993); 19) Cornwell et al (1996); 20) Cronin and Vann (2003) Thomas et al (2000Thomas et al ( , 2004; 55) Toyoda and Kitazato (1995); 56) Tsujimoto et al (2006a); 57) Tsujimoto et al (2008); 58) Turner and Rabalais (1994); 59) Turner et al (2004); 60) Turner et al (2006); 61) Voss and Struck (1997); 62) Willard et al (2003); 63) Yasuhara et al (2003); 64) Yasuhara and Yamazaki (2005); 65) Yasuhara et al (2007); 66) Zheng et al (2003); 67) Zimmerman and Canuel (2000); 68) Zimmerman and Canuel (2001); 69) Zimmerman and Canuel (2002) …”

“…In addition to the availability of datable sediment cores, requirements include a relatively sheltered, low-energy setting that permits the deposition of fine-grained sediments, a sedimentation rate that is sufficient to allow for the resolution of the events of interest, and limited bioturbation and taphonomic processes that do not destroy the record (Murray and Alve, 2002;Clarke et al, 2006). These conditions can be found in estuaries, on continental shelves off the mouths of major rivers, in fjords, and areas where tidal disturbances are minimal.…”

Hundred years of genetic structure in a sediment revived diatom population

“…Anthropogenic loadings of phosphorus (P) and nitrogen (N) have increased in Danish estuarine waters, especially since the 1950s (15). During the 1970s the input of P in the Mariager Fjord reached 80 tons per year, and an annual average phytoplankton biomass of 60 milligrams of chlorophyll a per liter was recorded.…”

Diatoms as indicators of eutrophication in the SW part of the Gulf of Gdańsk, the Baltic Sea

“…In the study area it was observed by Witkowski (1994), Witkowski & Pempkowiak (1995), Stachura & Witkowski (1997), Stachura (1999), Witak (2000), , Leśniewska & Witak (2008) and Witak (2010). This species was recorded also in the Gulf of Finland (Weckström et al 2004, Clarke et al 2006) and the Gulf of Riga (Olli et al 2008) and the Szczecin Lagoon (Bąk et al 2001). Another species representing the same genus is C. meneghiniana.…”

“…It was frequent in diatom assemblages preserved in the superficial sediments of the Gulf of Gdańsk (Witkowski 1994, Witkowski & Pempkowiak 1995, Stachura & Witkowski 1997, Stachura-Suchoples 1999, Witak 2000, Leśniewska & Witak 2008, Witak 2010. It was encountered also in sediment samples from the Gotland Basin (Andrén et al 2000a), the Bornholm Basin , the Arkona Basin, Oder Rinne and Greisswalder Bodden , the Szczecin Lagoon (Bąk et al 2001(Bąk et al , 2006, the Archipelago Sea (Tuovinen et al 2009), the Gulf of Finland (Weckström et al 2004, Olli et al 2008, the Gulf of Riga, the Kattegat (Olli et al 2008) and the Roskilde Fjord sediments in Denmark (Clarke et al 2003(Clarke et al , 2006. In the studied cores, C. atomus was quite abundant and its percentage content usually reached 3 -5%.…”