Relationships between land use and nitrogen and phosphorus in New Zealand lakes

Developing policies to address lake eutrophication requires an understanding of the relative contribution of different nutrient sources and of how lake and catchment characteristics interact to mediate the source–receptor pathway. We analysed total nitrogen (TN) and total phosphorus (TP) data for 101 New Zealand lakes and related these to land use and edaphic sources of phosphorus (P). We then analysed a sub-sample of lakes in agricultural catchments to investigate how lake and catchment variables influence the relationship between land use and in-lake nutrients. Following correction for the effect of co-variation amongst predictor variables, high producing grassland (intensive pasture) was the best predictor of TN and TP, accounting for 38.6% and 41.0% of variation, respectively. Exotic forestry and urban area accounted for a further 18.8% and 3.6% of variation in TP and TN, respectively. Soil P (representing naturally-occurring edaphic P) was negatively correlated with TP, owing to the confounding effect of pastoral land use. Lake and catchment morphology (zmax and lake : catchment area) and catchment connectivity (lake order) mediated the relationship between intensive pasture and in-lake nutrients. Mitigating eutrophication in New Zealand lakes requires action to reduce nutrient export from intensive pasture and quantifying P export from plantation forestry requires further consideration

Magnetization and static scaling of high-Tc disordered molecular-based magnet V(tetracyanoethylene)x¢y(CH3CN) with x ~ 1.5 and y ~ 2)

Journal ArticleWe report field (H) and temperature (T) -dependent magnetization (M) of a member of the new class of high-Tc molecular-based magnets V(tetracyanoethylene)x .y(solvent) with Tc in an accessible range (solvent =CH3CN). The M (H) at low T saturates slowly with increasing H. The random magnetic anisotropy model is applied to study the behavior of this disordered material, yielding values of anisotropy strengths and exchange constant. The results of an equation-of-state and scaling analysis near Tc are given and compared to theoretical results

Spin frustration and metamagnetic behavior in a molecular-based quasi 1-D-ferrimagnetic chain: (MnTPP)(TCNE)

Journal ArticleWe report an experimental observation of spin frustration and metamagnetic behavior in a quasi-1D ferrimagnetic chain, (MnTPP) + (TCNE) -. Metastability, hysteresis effects, and irreversibility of thermal and magnetic histories are observed in magnetization measurements. The "memory" phenomenon is seen in the temperature dependence of the thermoremanent and isothermal remanent magnetization. This system may be relevant to the magnetic behavior of the quantum/classical spin chains. The isothermal M(H) at T=2.25 K supports a first order transition which may be related to effects of local anisotropy

Ferromagnetic behavior and magnetic excitations in a molecular-based alternating-spin chain: decamethylchromocenium tetracyanoethenide

Journal ArticleWe report the study of magnetic properties of a molecular-based alternating-spin chain: metallocenium electron-transfer salt decamethylchromocenium tetracyanoethanide, [CrCp(*2)] [TCNE]. We give a modified spin-wave theory for the Heisenberg alternating-spin chains. The low-field susceptibility and magnetization data agree with the theoretical results indicating that one-dimensional linear magnon excitations dominate the magnetic behavior above the three-dimensional ordering temperature. Strong ferromagnetic intrachain coupling, J (=) 9 K, is found. Unusual critical phenomena associated with lattice dimensional crossover are discussed

Anomalous magnetoresistance in high-temperature organic-based magnetic seminconducting V(TCNE)x films

Journal ArticleAnomalous positive magnetoresistance (MR) in high temperature organic-based magnet V(TCNE)x (TCNE=tetracynoethylene) thin films is reported. MR increases linearly with applied magnetic field and shows a maximum at the ferrimagnetic ordering temperature. The suggested roles of oppositely spin polarized (pi)* electronic subbands and magnetization fluctuations due to the disordered nature of V(TCNE)x films are discussed

Optical properties of the 1:2 compound of dimethylferrocenium with tetracyanoquinodimethanide: [(Me2Fc)(TCNQ)2]

Journal ArticleWe present the results of a study of the room-temperature polarized reflectance of (1:2) 1,1'-dimethylferrocenium ditetracyanoquinodimethanide [(Me2Fc)(TCNQ)2] over the range between the far infrared and the near ultraviolet. Kramers-Kronig analysis of the reflectance is used to determine the optical properties of the compound. Vibrational features are evident at low frequencies whereas electronic excitations, including charge transfer between TCNQ molecules, are observed at higher frequencies

Dynamic spin fluctuations in the molecular ferromagnet (DMeFc)(TCNE)

Journal ArticleThe static and dynamic magnetic properties of the molecular ferromagnet decamethylferrocenium tetracyanoethenide (DMeFc)(TCNE) are studied via the muon-spin-relaxation technique. Spontaneous order is observed in the ferromagnetic ground state below 5 K, while the muon-spin-relaxation rate in the paramagnetic phase displays a gradual variation with temperature, indicating that a slowing down of spin fluctuations occurs over a wide temperature range. The temperature dependence of spin fluctuations between 8 and 80 K shows the thermally activated behavior expected in a spin chain with Ising character

Optical properties of quinolinium tetracyanoquinodimethanide, [Qn(TCNQ)2] and (N-methylphenazinium)x(phenazine)1-x (tetracyanoquinodimethane) [(NMP)x(Phen)1-x(TCNQ)]

Journal ArticleWe present here optical-absorption data of quinolinium ditetracyanoquinodimethanide [Qn(TCNQ)2] and (N-methylphenazinium)x(phenazine)1-x(tetracyanoquinodimethanide) [(NMP)x(Phen)1-x(TCNQ)] for 0.5 <_x<_ 0.6. These materials span the range of electronic structure from commensurate, to commensurate with confined soliton-antisoliton pairs (bipolarons), to incommensurate. The data show that these materials are semiconductors up to 300 K. The semiconducting gap, due mostly to a Peierls distortion, is weakly temperature dependent, decaying slowly as the temperature increases. This behavior, determined by the observation of the totally symmetric a, vibrational modes of the TCNQ molecule, is similar for all compositions studied and is suggested to be due to the effects of an external cation potential or to Coulomb effects, which vary little with composition. Substantial in-gap absorption is observed and is suggested to be due to the presence of quantum-nucleated and thermally generated bipolarons. The variation of higher-energy electronic transitions with composition corresponds to a crossover from commensurate to incommensurate electronic structure