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Internal and external loading as regulators of nutrient concentrations in the agriculturally loaded Lake Pyhäjärvi (southwest Finland) (1997)

Ekholm, Petri ; Malve, Olli ; Kirkkala, Teija

Springer

Hydrobiologia 345 (1997), S. 3-14

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ISSN: 1573-5117

Keywords: eutrophication ; phosphorus ; bioavailability ; nutrient balance ; agriculture ; models

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract This study assesses the effects of external and internalloading on the nutrient concentrations in an agriculturallyloaded shallow lake. Using 13 years of observations of thelake's input and outflow, we calculated the long-term balancesof Tot-P and Tot-N. A more detailed balance, which includeddissolved nutrients and suspended solids, was estimated for anice-free period of one year. The contribution of the externalload was assessed using a mass-balance model. The internalload was estimated from the nutrient balances and on the basisof sedimentation measurements and bioassays. The drainagebasin of the lake provided most of the external nutrientinput; the remaining load was derived from atmosphericdeposition to the lake. The proportions of river-transported Pand N in dissolved form were 25% and 77%, respectively. Thelake retained 〉80% of the external load. Particulatenutrients settled to the bottom and were probably resuspendedseveral times before permanent sedimentation. Dissolvednutrients were bound by primary producers and a highproportion of dissolved P was removed with the fish catch.Dissolved N was also lost via denitrification. Themass-balance model showed that external loading only partlyregulated the mean annual nutrient concentrations in the lake.The regulation was probably due to internal loading, which washigh despite the efficient net retention of nutrients. Duringthe ice-free period, the temporal variations in nutrientconcentrations were controlled almost solely by internalprocesses, such as resuspension of inorganic and organicbottom matter. Although the internal load of bioavailable Pmay, under favourable conditions, exceed the external load,the mechanism by which bioavailable P is translocated from thebottom sediments to the water could not be fully identified. Abbreviations used in this paper follow the editor'srules.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1002958727707

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Preparation of a novel HALS polypropylene stabilizer (1995)

Ekman, Kenneth ; Ekholm, Lars ; Näsman, Jan H.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 2699-2703

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ISSN: 0887-624X

Keywords: radiation ; grafting ; HALS ; reactive processing ; m-isopropenyl-α,α-dimethyl benzyl isocyanate ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The radiation induced graft copolymerization of m-isopropenyl-α,α-dimethyl benzyl iso-cyanate (m-TMI) and styrene onto polypropylene was carried out. The extent of grafting increased with increasing amount of styrene and with increased radiation dose. A graft load of 180% was obtained by immersing a 50 kGy pre-irradiated film in a monomer solution containing 25 mol % m-TMI and 75 mol % styrene. The graft copolymer is suitable for covalently binding nonpolymerizable stabilizers with a suitable nucleophilic moiety. In this work the isocyanate moiety of the graft copolymer was allowed to react with 4-amino-2,2,6,6-tetramethyl piperidine, a hindered amine light stabilizer. Fourier trans-formed infrared spectroscopy confirmed the formation of an urea moiety. © 1995 John Wiley & Sons, Inc.

Additional Material: 3 Ill.