Effects of shoreline development on the nearshore environment in large deep oligotrophic lakes

1. In large deep oligotrophic lakes, the shallow nearshore waters may provide the most important habitat for animals to feed and breed, and it is this area of the lake where humans are most likely to have initial impacts as the shoreline is developed. Nutrients in fertilizers, sediments and sewage effluents are likely to be rapidly intercepted by nearshore algae at the lake edge, having heterogeneous effects nearshore before offshore effects are noted. 2. Here we examined the spatially explicit effects of residential development on nearshore periphyton communities in three large deep oligotrophic lakes that have all experienced modest residential development in the Pacific Northwest of the United States. We demonstrate that substantial nearshore changes in the basal food web are detectable even with low levels of shoreline development. These changes can potentially affect whole‐lake food web dynamics. 3. For our primary study site (Lake Crescent, Washington, USA), we found that algal biomass and accumulation of detritus were higher at developed sites. In addition, both macroinvertebrate and periphyton communities exhibited a shift in composition with more detritivores and filamentous green algae at developed sites. These differences were more pronounced during the spring than at other times of year. 4. A complementary investigation of field patterns in Priest Lake and Lake Pend Oreille (Idaho, USA) suggested that, although spatial and temporal patterns were idiosyncratic, indicators of productivity and the presence of filamentous green algae were generally higher at developed sites across lakes. 5. Stable isotope signatures and water column nutrients were not useful in distinguishing developed and undeveloped sites, increasing the potential usefulness of periphyton monitoring during early stages of lake development. 6. A laboratory investigation suggested that common macroinvertebrate grazers assimilated a much greater proportion of diatoms than the filamentous green algae that are associated with fertilization at developed sites. 7. These findings have at least two clear implications: (i) periphyton may be used to detect human impacts before disturbance is evident in offshore monitoring programmes and (ii) nearshore impacts in response to modest residential development have the potential to disrupt lake food web dynamics.     

Canopy damage to native vegetation on the central coast of New South Wales: Current status and detection of future changes

Abstract Canopy damage to coastal native vegetation was surveyed at Norah, Wybung and Wamberal Heads and at Little Beach on the central New South Wales coast in 1987. This preceded the commissioning of an ocean sewerage outfall at Norah Head in 1988, but postdated the commissioning of other outfalls in the region. Damage to the canopy of shrub species was assessed at the whole-plant level using a visual score. The method of scoring for canopy damage was tested for repeatability between observers; the average deviation between means was 5%, and the maximum deviation was 10% of the value of the mean. Mean per cent canopy damage scored for shrubs of various species at these sites ranged from negligible to very heavy. Comparison between sites and aspects was limited to Banksia integrifolia. Stands of this species on the southern side of Norah and Wybung Heads had approximately double the canopy damage of those on the northern side; this difference was significant. To confirm the patterns of damage seen at the whole-canopy level, the fate of tagged shoots of B. integrifolia was followed for 4 months. These shoots were also more damaged on the southern side than on the northern side of the two headlands. Analysis of wind speed and direction at Norah Head showed that the southern side of the headland received substantially more strong winds (>21 km h^?1) than the northern side. Airborne salt spray is known to be carried mainly in winds above this speed. In cases where 20 or more individuals of a species were found at a site, mathematical models relating the canopy damage of each plant to wind exposure, distance from the sea, and slope were investigated. Of 15 such cases, 13 significant models were found, with exposure being the major significant factor in accounting for variation in the data. Distance from the sea was only significant twice, and slope not at all. The pattern of damage, and its relationship to wind speed, direction, and exposure, are consistent with salt-spray being the major cause of leaf and shoot death at these sites. The sample sizes necessary to detect future changes of given magnitude to canopy damage were calculated.     

Multidecadal to millennial-scale shifts in drought conditions on the Canadian prairies over the past six millennia: implications for future drought assessment

Three high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the Canadian prairies, show that shifts in drought conditions have prevailed on centennial to millennial time scales for at least the past six millennia. These shifts in mean aridity exhibit broad regional synchrony, with particularly pronounced shifts at all sites between ∼1700–2000 cal. yr bp and ∼3600–3900 cal. yr bp , as well as at ∼5400–5500 cal. yr bp for the two sites which extend back to at least 6000 cal. yr bp . The two Saskatchewan lakes exhibited significant coherence in both the timing and direction of these shifts, whereas inferred changes at the westernmost site in Alberta were significantly correlated to the Saskatchewan sites, but opposite in sign, and exhibited more high-frequency variation on the scale of centuries. The mechanisms behind these abrupt shifts in aridity are poorly understood, but may be linked to changes in oceanic–atmospheric interactions that influence the mean position of the jetstream and the associated storm tracks. Natural shifts in mean climatic conditions may accelerate with increasing carbon dioxide levels intensifying the likelihood of extreme droughts in North American prairies.     

DEVELOPMENTAL PROCESSES, DEVELOPMENTAL SEQUENCES AND EARLY VERTEBRATE PHYLOGENY

(1) We have put forth the position that evolutionary sequences can be deduced by an analysis of fundamental developmental sequences. Such sequences are highly conserved within a group and 'contain steps which are necessary to achieve a developmental fate'. The premise of our work then, is that such fundamental sequences do not arise de novo time and time again but can be traced back through their evolutionary history in organisms which contain portions of the sequence. (2) These highly conserved developmental sequences are in fact developmental constraints to evolution in as much as natural selection has not been able to discard them, but rather has utilized them in achieving evolutionary change. (3) We have demonstrated the ability to use developmental data by producing an evolutionary sequence for the origin of the vertebrates using the processes of neuralization and cephalization, the latter due primarily to the influences of the neural crest and epidermal placodes. The evolutionary sequence created, while not novel in structure, is distinct in that it was created solely by following a developmental sequence that is highly conserved among the vertebrates. The sequence is: (a) Chordamesoderm differentiates from the surrounding mesoderm and induces an overlying neural tube. (b) Through the influence of neuralizing morphogens, the neural tube differentiates into anterior (fore-, mid- and hindbrain) and posterior (spinal cord) parts. Cephalization has begun. (c) Cephalization proceeds via the development of two new populations of embryonic cells, the neural crest, a derivative of the neural epithelium and the epidermal placodes, derivatives of the ectoderm immediately adjacent to the neural tube. These two populations contribute significantly to the subsequent development of the vertebrate head including the skeleton, connective tissues, cranial nerve and sensory organs. Sequence (a) occurs in the most primitive protochordates and is one of the differences between the chordates and deuterostome invertebrates. Sequence (b) occurred next leading to a protochordate with a differentiated central nervous system, but lacking most vertebrate head structures. Sequence (c) signalled the beginning of the true vertebrates or branchiates (after the branchial arches which all 'vertebrates' share) since the production of a neurocranium, viscerocranium, cephalic armour, teeth and cranial peripheral ganglia was only possible with the acquisition of this developmental step.(ABSTRACT TRUNCATED AT 400 WORDS)     

Phytoplankton nutrient limitation in Colorado mountain lakes

SUMMARY. 1. Limiting nutrients for phytoplankton were studied experimentally in eight mountain lakes of central Colorado between May and November of 1984.
2. Five categories of phytoplankton limitation were identified: no limitation, N limitation, P limitation, concurrent limitation (stimulation only by simultaneous additions of N and P), and reciprocal limitation (stimulation by addition of either N or P). The phytoplankton communities of three lakes were primarily N-limited, one was primarily phosphorus-limited, and four showed primarily combined limitation (concurrent or reciprocal). Switching between categories of limitation was also observed within lakes. Nitrogen was the most frequently limiting nutrient; N, either alone or in combination with P, accounted for 79% of all observed instances of limitation.
3. Nine indices were tested for effectiveness in predicting phytoplankton limitation by N and P. The best indices for discriminating all limitations were ratios of dissolved inorganic N: total P (84% accuracy) and dissolved inorganic N:total dissolved P (80% accuracy). The effectiveness of these indices may be explained by the degree to which they represent N and P fractions actually available to the phytoplankton.