Study on Spatiotemporal Evolution of the Yellow River Delta Coastline from 1976 to 2020

The Yellow River Delta in China is the most active one for sea–land changes over all deltas worldwide, and its coastline evolution is critical to urban planning and environmental sustainability in coastal areas. Existing studies rarely used yearly temporal resolution, and lack more detailed and quantitative analysis of coastline evolution characteristics. This paper used visual interpretation to extract the coastline of the Yellow River Delta in year interval Landsat images for 45 years from 1976 to 2020, and analyzed the spatiotemporal characteristics of the coastline evolution through statistical methods such as calculating change values and change rate. The main results are as follows: (1) overall, the coastline of the Yellow River Delta presented a spatial pattern involving northern landward retreat and southern seaward expansion. Since 1990, the Yellow River Delta has entered a period of decline. In addition, the length of the artificial coastline increased by about 55 km; (2) in the Qingshuigou region, the land area and the coastline length increased first and then stabilized. The southeastern part of the Qingshuigou was in a state of erosion, while the northeastern part was expanding toward the sea along the north direction; (3) in the Diaokou region, the land area has been decreasing, but the reduction rate has gradually slowed down. The main conclusions are as follows: (1) through the research on the evolution model and mechanism of the coastline of the Yellow River Delta, it was found that human factors and natural factors were the two major driving factors that affect the evolution of the coastline; (2) a river branch appeared in the northern part of the Qingshuigou region in 2014 and became a major branch in 2020, which would affect the development of the coastal region of Chengdao. This study is important for better understanding the evolution pattern of the Yellow River Delta coastline and will help to provide guidance for coastline management and resource exploitation.

Elemental and isotopic signatures of terrestrial organic matter along the Delta coastline of Lena River (Laptev Sea)

<p>A complex multydisciplinary oceanographic research was carried out along 358 km transect along the Lena Delta coastline (DCL): 58 stations were accomplished in 7 days in early September 2009. Our study focuses on structure of bottom sediments, dynamics of suspended particulate matter (SPM), content of particulate organic carbon (POC), total nitrogen (ON), C/N value, stable carbon (δ<sup>13</sup>С) and nitrogen isotopes (δ<sup>15</sup>N). It has been found a close connection between channels morthology, tectonic features and distribution of bottom sediments, SPM, water runoff along the DCL.</p><p>Neotectonic movements happened about 6,000 yr BP led to uplift of the DCL western part, which caused  redistribution of river runoff to the eastern channels of the DCL. The boundary between these “tectonic” parts of the DCL is the submeridional fault, to which the Tumatsky Channel is currently confined. Shelf waters with salinity (S) > 20‰ penetrated to the channel mouth, causing formation of a frontal hydrological zone with increased gradients of thermohaline characteristics. Almost fresh river waters (S<1 ‰) are distributed along the eastern part of the DCL (EDCL), and brackish water are distributed to the west of Tumatsky Channel (WDCL). The differences in the SPM average content between EDCL and WDCL are only 1.5 times, but the density of the river net in EDCL is almost 3 times higher. The reason is a more intense sedimentation of the SPM, causing the DCL progradation to the east and northeast of Laptev Sea. This is supported by 2-fold decrease by SPM from the inlets of Sardakhskaya, Bykovskaya and Trofimovskaya Channels to their mouths. Only fine SPM remain in transfer from the central DCL to the mixing water zone “river-sea”. A circumterral narrow strip of sand-silt sediments formed along the DCL’s edge, and a vast field of relict sands is distributed near the northwestern elevated ledge of the delta (WDCL). Seaward direction from DCL sand-silt sediments are quickly replaced by silt-mud. The average POC content in EDCL and WDCL, respectively, is 1.6 and 2.7%; average C-13 isotopic signal is -26.5 and -26.0 ‰; average C/N values are 9.8 and 9.3. That is confirmed by similar terrestrial geochemical signature in the nearshore sediments adjacent to EDCL and WDCL</p><p>Acknowledgements. This study was supported by Ministry of Science and Education of Russia (project № АААА-А17-117030110039-2), the Russian Science Foundation (grants № 19-17-00058), the Russian Foundation for Basic Research (grants №№ 18-05-70047, 18-05-00559, 19-77-00016, 20-05-00545).</p>

Studying the present-day dynamics of Lena delta by space images

The dynamics of Lena delta coastline since the late XX century up to the present time have been studied using Landsat satellite data. The comparison of different-time images of morphologically different segments of the delta coastline has shown the major portion of the delta to be stable. Minimal changes have been recorded near the mouths of the branches carrying a minor portion of the Lena runoffthe Olenekskaya and Tumatskie. In the eastern part of the delta, near the mouths of copious branches Trofimovskaya and Bykovskaya, no changes have taken place, as well as in its western part, which is represented by a part of abrasion marine terrace embraced by the delta. In the southwestern part, in the Olenek delta, the delta coastline has been eroded with the erosion material transported eastward by along-shore current. Near the mouths of the Tumatskaya branch, the forms of marine accumulation are unstable, and the marine terrace in the northeastern part of the delta shows a minor local erosion. The periods of erosion in different delta areas are not synchronous and the eroded zones are not large in size. No increment in the land, nor shore progradation have been seen.

ENVIRONMENTAL DEGRADATION OF THE COASTAL ZONE OF THE WEST PART OF NESTOS RIVER DELTA, N.GREECE

The coastal zone is a transitory zone between land and sea. Due to its importance to man, not only for its high food production but also for recreation, sea transportation and industrial activities, coastal zone receives high environmental pressure from him. This paper deals with degradation phenomena of the coastal zone in the west section of the River Nestos Delta, North Aegean Sea, with special stress on the geomorphological changes in the coastline. The length of the coastline in this part of river Nestos Delta (the Kavala- Chrisoupoli part), from Nea Karvali village to the west, up to the river mouth to the east, is around 35 km long. This section constitutes the biggest and more extended sector of the Nestos Delta; it is the section where the main course and the various branches of the river were located, in the past. Along the coastal zone of this section of the delta many lagoons, sand bars, spits, barrier islands, washover fans, etc. were developed in its geologic past. Some of these geoforms still exist, but the majority of them have been destroyed by physical and/or anthropogenic interventions. Two of the last interventions are the diversion and entrenchment of the river to the east, in early 50’s and the construction of two high dams in the river course inland, in 2000. These human interventions deprived this land of flooding waters and sediments resulting in: (a) drying of most of the river channels and courses crossing this area of the river’s delta, (b) erosion of the coastal landforms and retreat of the shoreline in the majority of the delta coasts. There are, of course, a few places along the coastline where deposition and accretion are still taking place. In more detail, along the coastline taken into consideration in the present paper, one can meet: • stretches with high erosion rates, like the Akroneri Cape (spit), the inner coastline of Keramoti bay (Kokala -Piges coast), the Monastiraki coastline, etc, • stretches with high accretion rates like the Keramoti peninsula/spit, and • stretches at equilibrium or low rate of change like the barrier (spit) west of Akroneri Cape up to Nea Karvali coast and a short stretch of the coastline south-east of Keramoti peninsula. Comparing the Delta coastline of 1945 (from available aerial photographs) and the coastline of 2002 (from high resolution satellite images), before the construction of the Thisavros and Platanovrisi high dams (period 1945-2002), it has been estimated that: 88% of the delta and the adjacent coastlines has been accreted while only 12% has been eroded. In other words, there was a surplus of accretion by 76% and the delta was procreated. Comparing the Delta coastline of 2002 (from high resolution satellite images) and the coastline of 2007 (from high resolution D-GPS field measurements), after the construction of the dams (period 2002-2007), it has been estimated that: only 39% of the delta and the adjacent coastlines has been accreted while 61% has been eroded. In other words, there was a surplus of erosion by 22% and the delta began to retreat. This was due to Δελτίο της Ελληνικής Γεωλογικής Εταιρίας, 2010 Bulletin of the Geological Society of Greece, 2010 Πρακτικά 12ου Διεθνούς Συνεδρίου Proceedings of the 12th International Congress Πάτρα, Μάιος 2010 Patras, May, 2010 the great reduction (by almost 80%) of the river’s sediment load reaching to the sea. Thus, up to 2002, or so, the balance accretion – erosion in the whole delta coastline was positive, whereas after 2002 the erosion and retreat predominates in the delta’s coastline. The prevention of sediments and fresh water flooding in the delta area, has also affected the crops production in the fields in the vicinity of the delta as well as the fish output in the lakes and lagoons of the coastal zone.