NE Aspects Research Articles

Effect of changes in forest water balance and inferred root reinforcement on landslide occurrence and sediment generation following Pinus radiata harvest on Tertiary terrain, eastern North Island, New Zealand

Background: The frequent occurrence of storm-initiated landslides following harvesting of Pinus radiata D.Don in steep, Tertiary terrain, East Coast region, North Island, New Zealand, is of increasing concern. This paper documents the influence of tree removal and of replacement plantings on the canopy water balance and soil moisture regime when slopes are at their most vulnerable to landslide occurrence. Methods: At a previously established study site, rainfall, throughfall, and soil moisture data were collected before a mature stand of P. radiata was harvested. After harvesting, part of the study site was replanted with P. radiata at 1000 stems ha-1 and part with 500 stems ha-1. Relationships between hydrological changes and landslide occurrence are discussed in relation to planting density, site factors, root system development, silvicultural regimes, and alternative land use options for mitigating erosion in highly erodible hill country. Results: Following harvesting, soil moisture levels remained higher for longer than under a mature forest until rainfall interception and evapotranspiration returned to pre-harvest levels. This coincided with canopy closure, irrespective of planting density. After thinning, interception and evapotranspiration decreased, then regained the equivalent of a closed canopy 2 years later. Landslide occurrence was highest on slopes >25° and with a NE aspect. Sediment generation rates were highest in 2─4-year-old plantings, then decreased markedly with increasing tree age. Conclusions: Irrespective of planting density, P. radiata had little influence on the soil-water regime until canopy interception, evapotranspiration rates, soil-drying and recharge cycles returned to pre-harvest levels, coinciding with canopy closure. During this period, pore-water pressures at times of heavy or prolonged rainfall likely result in soil saturation and an increase in landslides. The progressive loss of root strength of the harvested trees had a secondary influence. The duration of the post-harvest period of heightened slope vulnerability to landslide initiation is a function of the combined influences of site factors on rates of tree growth and survival, and of the planting density regime on the canopy water balance and soil water content until the development of an effective live soil-root reinforcement system. For areas identified as high risk, the targeting of high-value timber species with longer rotation length, including consideration of coppicing species, would minimise the risk of slope failure at harvest. Very high-risk areas unsuited to rotational harvesting will ultimately require transitioning to a permanent indigenous forest cover.

The role of glass powder in concrete with respect to its engineering performances using two closely different particle sizes

AbstractOne aspect of this paper is to examine the role of glass powder minerals in creating the pozzolanic compounds with usefulness in replacing traditional ordinary Portland cement and effectiveness toward conserving earth resources. Besides this, the study analyzes the effect of two closely mentioned particle size (GP75 and GP63) with 0–20% substitution on the behavior of concrete. To validate the blended system serviceability with control, the results are analyzed with the three‐way data presentation. The properties of specimen at fresh and hardening stages are compiled for 7, 28, and 90 days of curing period. The results of the study with respect to control and blended mixes describe that workability is not varied significantly up to 20% inclusion and the pozzolanic activity of GP63 is higher than that of the GP75, as the SAI value observed is 87–117% and 81–108%, respectively. In terms of strength, it is the bunch of compressive, split tensile, and flexural strength behavior demonstrating that up to 20% substitution level the gain in strength is progressive. The static and dynamic modulus of blended mix shows no significant difference at 28 days with control concrete. Moreover, the combination of scanning electron microscopy, energy dispersive X‐ray micrography, and nondestructive mode of testing also features the accountability in this respect.

Power and the ‘autonomous’ principal: autonomy, teacher development, and school leaders’ work

ABSTRACT One aspect of instructional leadership is the work principals undertake in supporting and developing teachers’ skills and capabilities. This paper examines this aspect of school leadership within a climate characterised by increased principal workloads, heavy external accountabilities, pressure to improve student results, and heightened autonomy which included discourses regarding principals’ increased freedom in staffing decisions. The case studies within this paper focus specifically on principals’ work in relation to the recruitment and development of staff. Policy and discourse suggests that principals have the autonomy to recruit and build staffing teams to meet school needs and improve outcomes, though questions have been raised about how autonomous public schools can be a part of a wider system. This paper explores the role autonomy plays in leadership practices relating to staff recruitment and development. The findings contribute to a body of knowledge regarding the ways principals make sense of and enact their work under highly pressurised school improvement policy conditions.

Germination, survival, and early growth of three invasive plants in response to five forest management regimes common to US northeastern deciduous forests

The association between invasive plants and disturbance is well-documented. Most forest management regimes include disturbance (i.e., harvesting and fire) to improve regeneration of native plants, such as oaks. There is a need for land managers of northeastern forests to foster regeneration of native species without promoting invasive species establishment. We evaluated the germination, first-year survival, and growth of three exotic plants (Ailanthus altissima, Alliaria petiolata, and Microstegium vimineum) in 56 uninvaded forest stands located in five management regimes (control, single burn, repeat burn, diameter limit cut, and shelterwood) across two provinces (Appalachian Plateau, AP, and Ridge and Valley, RV) and two slope aspects (north-to-east facing, NE, and south-to-west facing, SW). These results were compared with the native Quercus rubra survival and growth under the same conditions. Two-hundred-fifty seeds and 30 transplants for each species were planted at each site. Germination, survival, and growth were measured three times over one growing season and analyzed using generalized linear mixed models.RV sites had more open canopies, lower soil fertility, and lower plant species richness than AP sites; NE aspects had higher soil fertility and plant species richness than SW aspects. The shelterwood sites had the most open canopies. Germination rates were below 25%, but lowest in the control sites and higher in the RV and on NE aspects for all three species. Survival was above 70% for A. altissima, M. vimineum, and Q. rubra but below 20% for A. petiolata, with little difference among province, aspect, or management regime for all three species. Survival decreased significantly between measurements. Microstegium vimineum grew the most of the three species. Microstegium vimineum and A. petiolata grew best in shelterwoods and better in the RV and on NE aspects. Ailanthus altissima had more root growth in the RV than the AP and the least root growth in the control sites. Quercus rubra survived better in the RV and best in the harvested sites, though growth did not differ among the management regimes. These invasive species are similar to many native species during the early stages of colonization; their germination, survival and growth are initially precarious and dependent on adequate resources (NE aspects) with minimal competition (RV province). Our results suggest that the likelihood of colonization by invasive plants could be reduced by keeping canopy openings below 15% and encouraging native understory competition with deer exclusion and artificial regeneration where native seed sources are depleted.

Nitrogen nutrition of beech forests in a changing climate: importance of plant-soil-microbe water, carbon, and nitrogen interactions

For 15+ years, a beech (Fagus sylvatica L.) dominated forest on calcareous soil was studied on two opposing slopes with contrasting microclimate in Tuttlingen, Swabian Alb, Germany. The cool-humid NE aspect of these slopes represents the majority of beech forests under current climate, the warmer and drier SW aspect represents beech forests under future climate conditions. The field studies were supplemented by investigations under controlled conditions. The research program aimed to provide a comprehensive understanding of plant-soil-microbe water, carbon and nitrogen feedbacks in a changing climate and a holistic view of the sensitivity of beech to climate change. The results of comparative and experimental studies underpin the high vulnerability of adult beech and its natural regeneration on calcareous soil to both direct climate change effects on plant physiology and indirect effects mediated by soil biogeochemical cycles. Mechanisms contributing to this vulnerability at the ecosystem and organismic level indicate a high significance of competitive interactions of beech with other vegetation components and soil microbial communities. Obvious forest management practices such as selective felling did not necessarily counteract negative effects of climate change.

Comparison of snowpack on a slope and on flat land focusing on the effects of water infiltration

Water infiltration of snowpack plays an important role in the formation of wet avalanches. Several studies have examined water infiltration of snowpack on flat land. However, because water flow has a directional component parallel to the slope in snowpack on a slope, the effects of water infiltration into snowpack may differ between flat land and slopes, where avalanches are more likely to occur. From January 2012 to April 2012, we simultaneously observed snow pits on flat land and on a slope (40° incline; NE aspect). The observations showed that MFr (the ratio of the total thickness of the layers composed of melt forms to the thickness of all layers of the snowpack) was, on average, 23% higher for the snowpack on the slope than for the snowpack on flat land, despite the slope's being a shaded side slope. The largest difference between the MFr of the slope and that of the flat land was observed in early March, when MFr was 99% at the slope and 46% at the flat-land site. We analyzed these observations using a one-dimensional multi-layer snowpack model proposed by Katsushima et al. (2009). The model included parameterization of the vertical water-channel process in snowpack. Based on the results, to represent the MFr at each site, the amount of water infiltrating through vertical water channels was estimated at 27.4mm (2% of the total amount of water provided from the snow surface) for the slope and 797.2mm (54%) for the flat land. Our results indicate that in wet-snow regions, differences in the water infiltration process can generate notable differences between snowpack on a slope and that on flat land.

Structures and improvisation for inquiry‐based science instruction: A teacher's adaptation of a model of magnetism activity

AbstractOne aspect of scientific inquiry that appears to be particularly challenging to learn is how explanatory models are developed and used in science. It is even more challenging to learn to teach through methods that engage young students in building and using explanatory models. In part, this is because to do so requires that teachers make real‐time instructional decisions in response to the ideas that students articulate. In this paper I present an example of a teacher who participated in a series of activities during a professional development course that guided her and her colleagues through the process of developing and revising an explanatory model of magnetic phenomenon. She subsequently transformed this series of activities to use with her elementary school students. Contrasting the series of activities in the elementary classroom to the corresponding professional development activities revealed improvisational instructional acts and shed light on aspects of the classroom context that necessitated and facilitated improvisation. In particular, this paper highlights the multiple pedagogical and disciplinary structures that teachers implicitly chose among when improvising. © 2009 Wiley Periodicals, Inc. Sci Ed 94:142–163, 2010

Morphometry of glacial cirques in the Cantabrian Range (Northwest Spain)

Two study areas were selected in the Cantabrian Range, in northern Spain, in order to analyse the morphometric characteristics of Pleistocene glacial cirques in a relatively mar- ginal glacial environment. The Western Massif of Picos de Europa (WMPE) (highest altitude at 2,596 m) is characterised by Alpine-like relief and a geological landscape mainly dominated by calcareous outcrops. The sierras of Southwest Asturias (SSWA) (highest altitude at 2,002 m) is a typical Palaeozoic landscape of Appalachian-like relief and is dominated by old erosion surfaces. A statistical analysis found few relationships between environmental factors (altitude, aspect and lithology) and cirque morphometry in the WMPE. Glacial cirque development in this area is therefore likely to be more influenced by structural processes (such as differential erosion and fractures) and karstic erosion. In contrast, a clear increase in cirque size is observed with increasing altitude in the SSWA. In both study areas, cirques are predominantly distrib- uted in areas with N and NE aspects, but particularly so in the SSWA which is of lower alti- tude than the WMPE. In the SSWA but not the WMPE, the horizontal dimensions of the cirques tend to increase more rapidly than the vertical dimensions, supporting the allometric model of glacial cirque development in this area.

Buoyancy Regulation by Hatchery and Wild Coho Salmon during the Transition from Freshwater to Marine Environments

AbstractOne aspect of diadromy that has received little attention is buoyancy regulation in fish moving between freshwater and marine environments. Because of density differences between the two water types, fish must alter their whole‐fish density (WFD) or they will become positively (float) or negatively (sink) buoyant as they change environments. This idea was first suggested over 80 year ago but has been largely overlooked by the scientific community. To explore how fish regulate buoyancy during this important transition, I measured WFD and lipid levels and estimated swim bladder volumes (SBVs) of juvenile coho salmon Oncorhynchus kisutch collected from freshwater and marine environments. These fish exhibited increased WFD with increasingly dense environments, suggesting active buoyancy regulation. Most of the WFD increase was attributable to decreases in SBV, although hatchery coho salmon also exhibited decreased lipid levels with increasing WFD. Hatchery coho salmon had significantly higher lipid levels than wild coho salmon in both freshwater and marine environments. These high lipid levels may impede the ability of hatchery fish to regulate buoyancy and may increase their vulnerability to surface predators. Furthermore, lipid levels that vary with both environmental water density and fish origin clearly complicate the interpretation of this variable during the important transition from freshwater to the ocean.

Electrical resistivity tomography monitoring of permafrost in solid rock walls

This article describes the first attempt to conduct electrical resistivity tomography (ERT) in solid permafrost‐affected rock faces. Electrode design, instrument settings, and processing routines capable of measuring under relevant conditions were developed. Four transects, with NW, NE, east (E) and south (S) aspects, were installed in solid rock faces between Matter Valley and Turtmann Valley, Switzerland, at 3070–3150 m above sea level. DC resistivity in the transects was measured repeatedly during the summer and compared by applying a time‐lapse inversion routine. Resistivity values were calibrated using observed rock surface conditions of thawed, damp rocks (1–8 kΩ m), deeply frozen rocks (18–80 kΩ m), and the transition from damp thawed to frozen rocks (8–18 kΩ m). Mean surface layer resistivities of transects respond to air temperatures below 0°C with a rapid increase by a factor of 1.4 to 2.9 from values of 12–15 kΩ m to values of 22–31 kΩ m. Rock layers at depths of 2–6 m display a general trend of resistivity decrease in summer, corresponding to a persistent thawing process. Their response to anomalously cool August temperatures occurs with a time lag of 2 to 4 weeks. Only transects E, NE and NW display persistent, high‐resistivity permafrost bodies (>50 kΩ m) mostly at depths of 6–10 m. The maximum thaw depth of a continuous thawing front above permafrost is 6 m. However, the ERT results emphasize the role of heat transfer by deep‐reaching cleft water systems. Thus permafrost occurs in lenses rather than layers. ERT provides rapid detection of ice and water distribution in permafrost‐affected bedrock.

Soluble N compound profiles and concentrations in European beech (Fagus sylvatica L.) are influenced by local climate and thinning

We assessed seasonal changes of total soluble nonprotein nitrogen compounds (TSNN) in adult European beech trees (Fagus sylvatica, L.) growing under different local climate during the growing season immediately following a thinning treatment and 3 years later. In both years, samples of leaves, xylem sap and phloem exudates from beech trees growing in thinned and unthinned (control) stands on a dry, warm SW exposed and a cooler, moist NE exposed site were collected in May, July and September. In May of both years, asparagine (Asn) and glutamine (Gln) were most abundant in leaves and xylem, respectively, whereas arginine (Arg) dominated in the phloem. In July, TSNN concentrations decreased in all tissues and sites, but differences in water availability between aspects were reflected in TSNN concentrations. In September, differences in the increase of Arg concentration in the phloem were related to differences in the onset of senescence between treatments. Thinning treatment increased amino compound concentrations of beech tissues in July on both aspects, particularly at the NE thinned site. It is supposed that, the N balance of adult beech is favoured by both, the thinning treatments as well as the cool-moist climate prevailing at the NE aspect.

Climate and forest management influence nitrogen balance of European beech forests: microbial N transformations and inorganic N net uptake capacity of mycorrhizal roots

The effects of local climate and silvicultural treatment on the inorganic N availability, net N uptake capacity of mycorrhizal beech roots and microbial N conversion were assessed in order to characterise changes in the partitioning of inorganic N between adult beech and soil microorganisms. Fine root dynamics, inorganic N in the soil solution and in soil extracts, nitrate and ammonium uptake kinetics of beech as well as gross ammonification, nitrification and denitrification rates were determined in a beech stand consisting of paired sites that mainly differed in aspect (SW vs. NE) and stand density (controls and thinning treatments). Nitrate was the only inorganic N form detectable in the soil water. Its concentration was high in control plots of the NE aspect, but only in canopy gaps and not influenced by thinning. Neither thinning nor aspect affected the abundance of root tips in the soil. Maximum nitrate net uptake by mycorrhizal fine roots of beech, however, differed with aspect, showing significantly lower values at the SW aspect with warm–dry local climate. There were no clear-cut significant effects of local climate or thinning on microbial N conversion, but a tendency towards higher ammonification and nitrification and lower denitrification rates on the untreated controls of the SW as compared to the NE aspect. Apparently, the observed sensitivity of beech towards reduced soil water availability is at least partially due to impaired N acquisition. This seems to be mainly a consequence of reduced N uptake capacity rather than of limited microbial re-supply of inorganic N or of changed patterns of inorganic N partitioning between soil bacteria and roots.

Punishment of the offending organ in biblical literature

AbstractOne aspect of the principle of "measure for measure" is considered—the idea that the offending organ is punished. This concept can be found in all the biblical genres: narrative, law, the prophetic literature, poetry, and the wisdom literature. The organs that are punished run almost the full length of the body, from head to toe. Sometimes the concept is invoked literally, sometimes only metaphorically. In most cases the punishment is heaven-sent; but there are no few incidents where human action is involved and even animals (twice). In every case, the principle serves a theological function, in that it corroborates the existence of reward and punishment in the world.

Synchronisation of the parasitoid <i>Centrodora scolypopae</i> with its host <i>Scolypopa australis</i>

Eggs of the univoltine passionvine hopper Scolypopa australis Walker (Homoptera Ricaniidae) are parasitised by Centrodora scolypopae Valentine (Hymenoptera Aphelinidae) The life cycle of the parasitoid and synchronisation with its host was studied in a gully near Hamilton over four years The parasitoid was usually univoltine overwintering in diapause as a prepupa and pupating when host adults were present in midsummer However above average summer temperatures in 1981 resulted in up to 60 of the parasitoid population on a sunny slope with a NE aspect pupating before winter demonstrating that the diapause was facultative Photoperiod was found to be a key factor in diapause maintenance

Landscape Influences on Potential Soil Respiration Rates in a Forested Watershed of Southeastern Kentucky

Soil respiration measurements conducted in the laboratory have been shown to be related to temperature and moisture, with maximum rates at soil temperatures between 25 and 40°C and soil moisture between −0.01 and −0.10 MPa. A preliminary study using forest soils from eastern Kentucky supported the previous research with soil respiration rates greater at 25°C than at 15°C, with differences in soil respiration rates related to sample site terrain characteristics. To further understand the factors that influence laboratory or potential respiration rates, we conducted a stratified sampling of soils from Robinson Experimental Forest in eastern Kentucky. Sampling was stratified by slope aspect, slope curvature, and landscape position. Potential soil respiration rates varied by slope aspect with NE aspects having greater rates than SW aspects. Rates did not vary by landscape position but did vary by slope curvature on SW aspects with concave curvatures having greater respiration rates than convex curvatures. Predictive soil respiration models based on both terrain attributes and soil chemical properties were created for both slope aspects. The relationships revealed that at this scale soil chemical properties play a more significant role in predicting soil respiration rates than terrain attributes. Models for the NE aspect were stronger than those for the SW aspect. The NE model created from a combination of terrain attributes and chemical properties included extractable Mg, extractable Zn, specific catchment area, and slope aspect (R2adj = 0.620). The SW model created from a combination of terrain attributes and soil chemical properties included extractable P, extractable Zn, and tangential curvature (R2adj = 0.413).

Study of hail density parametrizations

AbstractOne aspect of hailstone growth that has received attention over the last twenty years is the importance of low‐density riming growth in hail. Density is an important parameter in riming growth because it regulates hail size and is also involved in other atmospheric processes, like crystal multiplication, charge transfer, etc. New numerical dynamic and cinematic models take into account the variability of density with growth parameters (such as size of cloud droplets, impact velocity and surface temperature) in order to attain more realistic results. These kinds of models need to have a function that describes the real low‐density riming process.Analysing previous results, it is clear that several different empirical parametrizations are employed to describe density. These parametrizations relate density to growth parameters through the variable X=Vob/Ts, where Vo is the impact velocity of droplets into the target, b is the droplet size, and Ts the hail surface temperature.These empirical expressions give different density values for identical growth conditions. It is important to note that these parametrizations stem from experimental data obtained in very different growth conditions and with different collector geometries.Working with experimental density data, we can show that different parametrizations are equivalent if X is defined in an appropriate way (taking into account correct impact velocity and collector geometry). Different environmental conditions are taken into account by means of Stokes' parameter.Due to this finding, we have aimed at developing a parametrization to be used in cloud models, which satisfactorily represents all experimental results. Copyright © 2002 Royal Meteorological Society

Processes regulating watershed chemical export during snowmelt, Fraser Experimental Forest, Colorado

In the Central Rocky Mountains, snowfall dominates precipitation. Airborne contaminants retained in the snowpack can affect high elevation surface water chemistry during snowmelt. At the Fraser Experimental Forest (FEF), located west of the Continental Divide in Central Colorado, snowmelt dominates the annual hydrograph, and accounts for >95% of annual stream water discharge. During the winters of 1989–1993, we measured precipitation inputs, snowpack water equivalent (SWE) and ion content, and stream water chemistry every 7–10days along a 3150–3500m elevation gradient in the subalpine and alpine Lexen Creek watershed. The study objectives were to (1) quantify the distribution of SWE and snowpack chemical content with elevation and aspect, (2) quantify snowmelt rates, temperature of soil, snowpack, and air with elevation and aspect, and (3) use change in upstream–downstream water chemistry during snowmelt to better define alpine and subalpine flowpaths. The SWE increased with elevation (P<0.001) and was greater on NE aspects (P<0.05). Subalpine soils were unfrozen. Snowmelt occurred throughout winter at low elevation (3150m), SE aspect stations. By snowpack peak water equivalent (PWE), the snowpack lost about a third (0.24m) of its moisture. The subalpine snowpack had warm (>− 3°C) temperatures throughout winter which resulted in significant snowpack ion loss. By snowpack PWE in mid May, the snowpack had lost almost half the cumulative precipitation H+, NH4+, and SO42− inputs and a third of the NO3− input. Windborne soil particulate inputs late in winter increased snowpack base cation content. Variation in subalpine SWE and snowpack ion content with elevation and aspect, and wind redistribution of snowfall in the alpine resulted in large year-to-year differences in the timing and magnitude of SWE, PWE, and snowpack ion content. The alpine stream water ion concentrations changed little during snowmelt indicating meltwater passed quickly through surface porous soils and was well mixed before entering the stream. Conversely, subalpine stream water chemistry was diluted during snowmelt suggesting much melt water moved to the stream as shallow subsurface lateral flow.

Collembola of loess grassland: effects of grazing and landscape on community composition

In loess grasslands, grazing by sheep is responsible for changes in the composition of vegetation and controls on secondary successional processes. Grazing has a very complex effect on the soil by altering its physical, chemical and biological properties, which makes it difficult to distinguish the underlying mechanisms. Landscape heterogeneity also influences soil and vegetation processes, having a greater effect on environmental factors than sheep grazing. To compare the relative effects of sheep grazing and one aspect of landscape heterogeneity on the collembolan community, four valleys with two grazing treatments were selected. The sides of each valley had SW and NE aspects resulting in two types of landscape heterogeneity. In a split-plot experimental design, the effects of grazing pressure and aspect were examined in relation to the relative abundance, species richness, evenness and composition of the collembolan community. Grazing pressure had a positive effect on total abundance and a negative effect on species richness of Collembola. Aspect did not significantly influence total abundance but valley sides exposed to SW had a higher species richness. Grazing changed the dominance structure, reduced the evenness and strongly influenced the composition of the collembolan community. Due to grazing xerotherm epedaphic species disappeared resulting a less diverse Collembola fauna. Aspect had a lesser effect on collembolan community composition than grazing. The results suggest that the diversity of springtails maintained by landscape heterogeneity in loess valley sides is reduced by sheep grazing. Further, differences in soil humidity could not explain the changes in structure and abundance of the collembolan community alone, sheep grazing may drive changes in collembolan community through mechanisms of biotic effects.

Change in snowpack, soil water, and streamwater chemistry with elevation during 1990, Fraser Experimental Forest, Colorado

Every 7–10 days during the winter of 1989–1990, we measured precipitation ion input, snowpack water equivalent (SWE) and ion content, soil water and streamwater chemistry along a subalpine to alpine elevation gradient in the Fraser Experimental Forest (FEF), Colorado. The objective was to quantify the effect of elevation and aspect on snowpack ion accumulation and loss, and relate these processes to subsequent change in soil water and first-order stream chemistry during snowmelt. SWE increased with elevation ( P < 0.001) and was greatest on NE aspects ( P < 0.001). Snowpack ion concentration increased with elevation, with NH 4 + and NO 3 − showing the most consistent ( P < 0.05) increase throughout winter. Snowpack base cation (C B) and S0 4 2− concentrations were significantly higher on NE aspect transects. In most weeks, the snowpack NH 4 + and NO 3 − content was highest ( P < 0.05) in the alpine zone. Peak snowpack NH 4 + and NO 3 − content totalled more than 1 kg inorganic N ha −1. Alpine soil water NO 3 − concentration during and after snowmelt was greater ( P < 0.001) than at lower elevations. However, there was no significant correlation between weekly snowpack ion loss and soil water chemistry. At the FEF, it seems that most snowmelt is routed through the watershed as subsurface flow. Soil processes such as ion exchange, biological uptake, overwinter nitrification and mineralization are probably major factors modifying melt water chemistry. There was no correlation between soil water chemistry and streamwater chemistry, which probably reflected the high variation in distance and time required for soil water to reach the stream.

Phytoplankton — Community Structure, Succession and Chlorophyll Content in Lake Müggelsee from 1979 to 1990

AbstractOne aspect of the present work on Lake Müggelsee has been a quantitative assessment of phytoplankton changes over the annual cycle and from year to year as a basis for primary production measurements. The investigations of plankton analysis were carried out in Lake Müggelsee (Großer Müggelsee, Berlin), a eutrophic, polymictic shallow lake with an area of 7.2 km2, a mean depth of 4.9 m. The lake was described as a species rich water with partially considerable developments of diatoms and blue‐green algae as was shown by plankton analyses from the beginning of this century. Since the end of the 60s, when macrophytes disappeared, Lake Müggelsee has been recognized as a lake with extensive phytoplankton development characterized by dense and irregular development of blue green algae and diatoms. Especially solitary centric diatoms increased in number and in biovolume from 1979 to 1990 and occurred with greater diameters in spring during the seasonal course.The specific content of chlorophyll a was estimated according to the algal composition. It is suggested that the observed decrease in Chl a per unit biovolume is associated with species size rather than the time of development depending on the unknown portion of inactive algal cells resuspended from the sediment surface.